The issue here is opportunity cost. It has nothing to do with difficulty. The time spent porting to Python 3 has to provide a better return on investment than the same time spent doing something else. For a lot of people for a very long time, continuing to now 12 years later, that opportunity cost was such that porting to Python 3 was always a lower priority.

Languages need to serve their users, not the other way around. A lot of us really didn't care about minor syntax tweaks and we didn't need a lot of the new features. What we needed was better performance and a better deployment story, and we have received neither.