I do not know what is wrong with Python, because I use it only occasionally, for short programs that do not use obscure features.
Nevertheless, there is no doubt that it is the worst software project that I have ever seen, during several decades, from the point of view of keeping compatibility between versions.
For other programs, I may happen to need to have installed 2 versions, or maybe 3 versions, at most, in order to be able to use other programs that are compatible only with certain versions.
On the other hand, for Python, during many, many years, I have been forced to keep installed all the time around 7 or 8 versions, to keep happy many other programs that claim to be compatible only with certain Python versions (and not also with any newer versions; some programs are even compatible only with a list of non-consecutive versions).
Building from source any program that depends on Python may frequently require various temporary configuration modifications, to ensure that the program is built only for the Python versions with which it is compatible.