Ubuntu is actively working on the transition but the current LTS release (ie the one companies/enterprise will use) is still locked onto python2.
The same can likely be said for other flavors of *nix.
From a user's perspective, python3 has been ready for 'prime time' for a while. From an OS, systems, enterprise perspective python3 still is still a ways out.
If you maintain many FOSS libs like I do, together with tox it's priceless.
What if I want to distribute a package to an audience that doesn't have a strong Python background.
What would otherwise be a simple 'pip install' just turned into a complex multi-step process to install a new version, update PATH, and use virtualenv to avoid conflicts with the default install used internally by the OS.
These all seem like 'simple' fixes to a regular Python user but they set a huge barrier-of-entry for others.
'Just use [insert python specific fix]' is a UX failure for a language that emphasizes usability.
To reiterate. Python3 is ready for regular python users/devs. Not so much for the rest who consume python applications.
We're mostly seeing the same thing, but there is a few libraries where we maintain forks, because the original author didn't test Python 3 support, but just claimed that it would work. However all but one of these libraries are by commercial companies an solely for integrating their service. For the third one the original author seems to have evaporated (I believe one of my colleague are planning a fork with some of the other users of the library).