They could have, but they didn't want to.
It's an open source project. Is there really much of a difference between "I'm not going to work on this system because it's terrible" and "I'm forking this system and I'm not going to support the previous version"?
In both cases you can say "well someone else will just come along and support it", and for py2 they did, for a bit. In fact I believe you can still pay if you happen to want py2 support.
But if you're not paying, you're saying "hey, this thing you work on and provide to me for free - why are you working on it in the way you want rather than the way I want??"