Calling any Python programmer here (especially package maintainers)

I run Gentoo, so am responsible for maintaining the dependency tree (to a degree). When it comes to Python I have 2.7, 3.4, 3.5, 3.6 available. I'm always running into some package needing one version or another, and I can't just set a single version and forget it (which is fine. I'm running Gentoo).

I know that this is because python changes rapidly and so different libraries need different versions. Fine.

Why does this happen with Python and not C++, JavaScript, php, ruby, or any other languages on my system? I don't have 3 different versions installed to cover any other languages, and I don't spend time adding installation rules to cover them.

Why does Python need to be a pain in the ass about it?