>>723751405 (OP)
Game engines.
I mean this seriously, I'm not saying that game engines are bad but they killed the need for cooperation. Before game engines was openly avaliable and good enough, you needed to write your own libraries, cross platform support, tooling, sound system and so on.
Want to make a game? You _needed_ to know people, you needed these people to help and as a result everything was a collaborative effort.
Today? 10 people in the past who'd have settled on a single project and worked together, are all now wanting to make their own game. They can't get help because "why should I work on your game idea when I could work on my game idea" and other similar lines of thinking. Because it's possible to create your own game on your own, the collaborative nature of it is gone.
Especially in the communities. The indie dev culture is very individualistic and never actually producing anything as a result of free engines for ages. Game engines made everyone individualistic.