Because ecosystems are driven by mindshare (popularity), convenience, adoption potential barriers, public shaming (eww, that's nasty, but .. people are people), and other psychological micro-foundations. Basically it's a cold war of persuasion. Sometimes leading by example works, sometimes by showing how awesome, cool, fast, safe your shiny stuff is, sometimes it works by appealing to people's sense of the "greater good" (how many Korean, Chinese, Iranian, Saudi, etc. democratists are in secret prisons, because broken C code).
And of course there's some truth to it. Look how Py2 is still not dead, because rewriting twisted is hard. (Which no one said it was easy.) And how long it took for distros to make it the default, and how long it took for anyone to not default to it. And of course there were people even complaining about how Py3 broke all their nice code that worked before by accident.
So if collectively everyone had made a push some years ago, we would be long over. But of course organizing these things is an even bigger problem than just sitting down and firing off PRs to twisted.
And of course there's some truth to it. Look how Py2 is still not dead, because rewriting twisted is hard. (Which no one said it was easy.) And how long it took for distros to make it the default, and how long it took for anyone to not default to it. And of course there were people even complaining about how Py3 broke all their nice code that worked before by accident.
So if collectively everyone had made a push some years ago, we would be long over. But of course organizing these things is an even bigger problem than just sitting down and firing off PRs to twisted.