again, this makes no sense. I don't make the rules, UA does. Under its own rules, UA allows me to select seats when I book my trip, and to change them after I purchase my ticket. If I am elite then UA does not charge me a seat rez fee. So under the existing rules I am free to book all aisles for my entire family. Or all windows. Or all middles. Or whatever combination I want. There is nothing in the contract or MP rules that restricts my choices.

If UA does not want people to book aisle and window seats (leaving open middles) it is free to restrict that option through technology, or by charging additional fees, etc. But it needs to provide honest and transparent disclosure of this "rule" to its customers so that we can make informed decisions.
If this is the path that UA chooses, I may very well choose to book another airlines even it costs me more money, because seat location is a very important factor in my purchasing decision.

The sneaky underhanded seat changes, without any notice to the customer, are not honest or transparent, nor are they good business practice because they offend the airlines best customers. if - as you suggest - i'm not a "good customer" because I buy tickets on UA (and not WN) in part based on the promise that I can reserve E+ seats - then maybe UA should change its rules. I am not "forcing" a stranger into a middle seat. Pre-COVID I would often SDC my flights and take a middle seat if it was the only one remaining. It never in a million years occurred to me that some unknown fellow passenger "forced me into a middle seat". That is just the seat that when I purchased my ticket on that flight.