I think the general dicking around that you could do with friends in multiplayer is a dying animal, but that is good and bad. More people want to play competitive multiplayer and that can extend the games multiplayer for hours on end, whereas you dicking around with you friends could last a weekend or two, hell maybe three. But eventually (or in my experience) want to move onto something else and the game gets shelved.
For example I bought 50 Cent Blood in the Sand, and in my opinion it is one of the most hilarious split screen games you can play with another person. Just over the top silliness and you get your money's worth from the game. But after a second play through my friend and I were pretty much done with the game and we moved onto something else. But something like MW2 I think I've logged around 100 hours and I've derived another kind of fun from playing it competitively and if it wasn't for the removal of being able to choose random gametypes each match I would've logged 100 more hours.
It really wasn't a change over night, its just a change of the times. A lot of people played games doing split screen because there was no online multiplayer or not everyone could afford a console/game at home. Hell I remember the obscene hours I spent at LAN centers playing counter strike with like 30 other guys from highschool every other day. And we just dicked around the whole time. But with the availability of home computer and high speed internet those days are gone. And makes me comes to a realization a lot of the fun of playing is that you're playing with people that you know and even if you're losing you can laugh it off with the person that you know who is beating you. But with online multiplayer being pretty anonymous and your odds of meeting those players again it becomes a real hard loss to take and you really can't laugh it off. So it might be that multiplayer really hasn't lost its point at all, but the circumstances around the game have changed how players respond to it.
