Python 3 is now used in 36% commercial projects
semaphoreci.com
semaphoreci.com
Look at many other languages, php, ruby etc. They make breaking changes and give the users a choice. If you want the new features, you'll have to upgrade. PHP7 for example, has been out for about 2 years now and almost have 10% usage already. It's not great, but I think the upgrades will go a lot faster than in the Python community as libraries and frameworks move to the new version and completely stops supporting the old.
I think that is a better path for tools like programming languages instead of making new stuff for two different versions. People are lazy, companies even more so. If there is no reason to update they won't.