Because we live in a society where the incentives are not conducive to collaboration. Imagine if everyone had a UBI, and you contributed fixes and improvements

Because we live in a society where the incentives are not conducive to collaboration. Imagine if everyone had a UBI, and you contributed fixes and improvements to a project because you thought it was cool. That's how professors with tenure for centuries rushed to publish scientific articles, for instance. In fact, in antiquity, we had the opposite problem to what you describe ... often things were credited to a certain leader of a school (e.g. Pythagoras) even if he didn't invent them. The problem is that people are thinking about how to make a profit, and it's ubiquitous because it's wrapped up with trying to survive, at all. By the time you make millions of dollars, you still have the PTSD from trying to outrun the bear, you keep going by inertia and making billions. Competition is far less healthy than collaboration. It's what causes the countries on earth to speed towards AI apocalypse for instance, or fossil fuel apocalypse, etc. The few times they cooperated (e.g. Montreal Protocol, or nonproliferation of chemical weapons) has been a resounding success. I doubt they'll be able to come together like that for AI, though!