Because there's been not enough carrot and too much stick.
The only real killer feature of Python3 is the async programming model. Unfortunately, the standard library version is numbingly complex. (Curio is far easier to follow, but doesn't appear to have a future.)
On the down side, switching to Unicode strings is a major hurdle. It mostly "just works", but when it doesn't, it can be difficult to see what's going on. Probably most programmers don't really understand all of the ins and outs. And on top of that, you get weird bugs like this one, which apparently is simply never going to be fixed.
The only real killer feature of Python3 is the async programming model. Unfortunately, the standard library version is numbingly complex. (Curio is far easier to follow, but doesn't appear to have a future.)
On the down side, switching to Unicode strings is a major hurdle. It mostly "just works", but when it doesn't, it can be difficult to see what's going on. Probably most programmers don't really understand all of the ins and outs. And on top of that, you get weird bugs like this one, which apparently is simply never going to be fixed.
https://github.com/pallets/click/issues/1212