Meanwhile on the more serious discussion
I agree that in the cases you described, someone was asking for something they're not entitled to and (especially if flying enough to be Gold, Plat, CL, etc) should have known they're not entitled to.

Lounge access after a J flight and before a Y flight, however, is something that's asked regularly in airline fora on FT, so clearly it confuses some people. For some, it may be their first time in J and they've bought the marketing hype that flying business class means red carpet treatment throughout. Asking, I think, it understandable; arguing, of course, is not.

Similarly, the rules for guesting at lounges is complicated and I think it's reasonable that people might ask. My QF-Plat colleague tried to guest me into the EK DXB First lounge even though we were on different flights. He's not pushy or difficult, he just was more familiar with QF rules than the EK rules.
But this is where the point that "passengers don't know the details of your business arrangements" kicks in. If someone is sitting at the EK desk wearing an EK badge checking in passengers for an EK flight (or controlling access to an EK lounge, or collecting BPs at the top of an EK jetbridge), then they are the face of EK as far as the passenger is concerned. If EK cares about its reputation, it needs to understand that, not just hide behind "they're not really our employees".
And here is where the complexity I described earlier comes into play. Two examples from my personal experience:

My first EK flight was Australia-Europe in the first month of the EK-QF partnership; at the time I was a paid Qantas Club member. I wrote after the trip:
If you’d been standing behind me at the time, I may have come across as someone who was "well aware there's no access" and who "wants more than what he or she is strictly entitled to." You may have shown your EK Gold or Platinum card or J BP and disappeared into the lounge, laughing at the pathetic Australian trying to game her way into your lounge. But in fact (a) the rules were confusing, (b) the rules were new and (c) the lounge agent was wrong. In this case, because I was prepared and persistant, she discovered her mistake and apologized.

Fast forward one week though, and they were still confused and not nearly as polite:
Again, I had to stand my ground and argue, but not because I was trying to get something undeserved, but because the staff didn't know the (still confusing) rules. Maybe they personally hate the QF partnership. Maybe they've been told to use any excuse to keep QC members out. Maybe it's just easier to say "no" and hope I'll go away than to check the actual rules. By the time I went back to DXB I was EK Silver so I never found out if they changed the rule.

My second example is EK Gold access at QF domestic lounges. I've now let my QC membership lapse since – I was told - EK Gold would also allow QF lounge access. For the first few months, at 5 different airports, I showed my EK Gold card and QF BP with QF FF number and entered the lounge. This is consistent with the (somewhat convoluted) wording on the QF website.

Then early this year, the lounge attendant at SYD pulled me up with "Oooh, no, no, NO! Not with a QF FF number - you have to have your EK number on the booking!" She followed up with "It's always been this way" and "all the airports do it", despite my earlier experience at ADL, PER, CBR, MEL and even that exact lounge in SYD. From behind the counter, she produced a laminated sheet of "special instructions" as proof which were quite different to the website text, and called her supervisor to come down and explain it all again to me. I'd only had 5 - 10 minutes spare before my flight, and this discussion had consumed that; on my return flight I grudgingly let them change the FF number.

I rang QF FF the next week and the woman there said that the lounge agent was wrong, it shouldn't matter which FF number. She even checked with HER supervisor to confirm. But the FF desk was unwilling to contact the lounge staff to discuss, so the next trip I got the same treatment at the lounge.

It's still not clear who's right. But one part of the airline says one thing, another says the opposite, they won’t communicate with each other, and I’m stuck in the middle. The website still supports my POV. Yeah, they’re minimizing costs by keeping me out of the lounge (except that my colleague came out and guested me in anyway). But minimizing costs by denying something a customer is allowed is poor business.

I have other examples (AA lounge/LAX/QF Gold, Air Pacific lounge/Fiji/QF Plat) but they’re much the same. Various combinations of operating airline, marketing airline, lounge operator and FF program lead to confusion.
I don't disagree with your overall point about revenue management. I don't imagine that my just-barely-Silver travel on QF domestic or my 2 – 3 trips/year in EK Y are anybody’s priorities. I don’t, to be honest, pay a lot of money. I just want what I’ve paid for (or earned via status).

But I think you are only looking at the case where “computer says no” and the computer is right. In my examples, the lounge attendant said “no” and was either wrong or was at least contradicted by others in the same airline. The customer is not always right, but they’re not always wrong, either.

And one final experience on moving to earlier flights. For many years I did 10 or 12 day trips/year on QF domestic, usually on the cheapest Y fare. Often it was a route with flights every hour or every half-hour. Without fail, if I was at the airport early for my return, the check-in agent would proactively offer to move me to an earlier flight, very often a “run now and you’ll just make it” choice.

Then suddenly they stopped. I would be at the airport 2 or 3 hours before my scheduled flight and politely ask “Is it possible to get on an earlier flight?” The agent would look at my booking as if it was a dead skunk, say “Oh, no, this is a CHEAP ticket, you can’t change THAT,” shove a BP at me and go to the next customer. Presumably some internal policy changed. Fine, they’re entitled to do that. But there’s no need to be rude about it.

I’m sure I don’t understand all of the actual costs involved in moving me from one 35 minute flight with a cookie and juice to another 35 minute flight with a cookie and juice. But I’m fairly confident I can work out the probability of them selling an expensive walk-up fare on the flight leaving in “run now and you’ll just make it” minutes versus selling a walk-up fare on a flight in 3 hours.

Most recently, I’ve booked flexible fares for my return. Now the policy is that they can’t change those either; I’m meant to ring my TA while standing in line and get them to re-issue the ticket! And again this has been explained quite rudely as if it should be obvious.

I’m not asking for what I’m not entitled to, but as “what I’m entitled to” seems to change without notice (or from person to person within the company), I think “I’m sorry, we used to do that but our policy has changed.” or "The rules are new; I'm not sure, let me check for you" would be better than treating me like I’m a criminal for asking.