Because most people's principles goes out the window the moment sticking to them becomes slightly inconvenient so companies are allowed to get away with it.

Well... actually yeah. I was inadvertantly accepting the enshittification.

Perhaps my cinema ticket could pay for the movie without also subjecting me to advertising, that'd be even better.

Money. Businesses want money.

It's not uncommon for people to just sit whenever they duckling feel like around here, assumed seating or not.

I'm old enough that I remember going to my local cinemas and there being no assigned seating. This was the norm. It did actually suck if you were "late".