What happened to intermissions?

So, I saw the Avatar 3 movie, in 3D in an IMAX theater. And I liked it (don't judge me, I understand the shortcomings, but I like the spectacle and the world-building). One thing that seriously detracted from me enjoying the movie was that it is 3 and 1/4 hours long. Including the bloody adverts in the beginning, that was some 3 3/4 h sitting on my ass.

I would say that a lot of people, me included, think that this is unreasonably long, to be without a bathroom break. I cannot imagine, how would I do that in 20-30 years, as my bladder becomes less trusty than now (which I dare say is quite normal for most older people). I am not even taking into account people who have problems sitting so long on one spot (thrombosis, etc.)

Thing is - I actually don't want the movie(s) to be shorter. Why cannot we make an intermission - a 15 min break in the middle? I am sure that the movie theaters would make more money that way - popcorn and cola surely bring them at least the same amount of money as the tickets themselves, nowadays. I am not a bloody director or a screenwriter, but I am sure that an organic intermission could be included into virtually any movie that is let's say over 2,5 h long. Wouldn't it be nice to take a pee, discuss the movie so far with a friend that is watching with you and stretch your legs? Why are we doing this instead?