Your expectation does not reflect the reality of the process flow or the fact that the Marriott Points System and the Hotel Systems are not integrated to allow what you suggest. Sadly, there are people involved, lots of different property management systems, and different processes at different properties that make this a far from seamless exercise.

Now that said, I have no idea why this points posting timeline is such an issue for so many people, or is it just an issue for FT-ers looking for something to complain about on the internet?

I for one am not sitting on my Bonvoy Points account 24/7 like I'm hatching an egg. I will do a periodic check-in to make sure all my stays have posted and write in if required, but I don't need immediate gratification nor do I wind up with severe anxiety of my points aren't posted within 3 days of my stay, cursing out the criminals at Marriott and railing on about how I've been "Bonvoyed" again.

I can understand particular situations where one might be needing points from one stay to book another, but I would think those cases are fewer and further between than the amount of complaining about slow posting would suggest.

My advice to all: It is what it is, accept it as you can't change it, no matter how many posts you make about it on FT.