It needs time ... but Python 3 was introduced twelve years ago!
And therefore after Ren'py started.
As long as Python 2.x was still in development, there were no need to switch to Python 3.x. Especially since Ren'py had first to wait for PyGame to be ported on Python 3.x, what only happened 8 years ago.
Then as long as it was maintained, the transition have been done slowly with the help of __future__.
Most changes are on this level and don't require much adjustment.
"Most" don't mean all.
Python 3.x was developed in parallel of Python 2.x for a very good reason : They decided to break the backward compatibility in the core of the interpreter.
And since they were going this far, already rid of the said backward compatibility, they jumped on the occasion to fix some issues with, among other things, some of the build-in function, changing either their arguments or part of their behavior.
Thinking that there just few syntax changes to do, and that your Python 2.x code will works with Python 3.x is an illusion ; especially for an application as complex as Ren'py with more than 400 000 lines, and that need to works on three different OSes, and now in top of that two different architectures for each OSes.
But all this said, what exactly is the purpose of your comment ? I'm not PyTom, and I doubt that he come here.