Linux Distros are always behind, and in the case of Ubuntu / Debian Python is locked into whatever they release because the OS actually relies on whatever version of Python they released the OS with, if you upgrade to latest and greatest on Debian Wheezy e.g. you might find your OS has bugs that Ubuntu 16.04 doesn't see (both use similar packages).

Really i use the latest and nightly gcc toolchain in ubuntu without issue, for python if what your saying is true could you not use conda or docker?

I guess it's mostly for interpreted languages. Try installing (not that I use it) Eclipse the Java IDE as another example, it's usually dated enough. This is probably why people use bleeding edge distributions. I guess in the case of compilers it's not as bad, though you can't usually get the latest and greatest Go compiler either, you have to grab the .deb off the website or use other tools. At least Rust just hands you rustup so I don't need to worry about this in the case of Rust, but with other languages like Python it's a concern of mine.

You can with Guix(pkg mgr or GuixSD distro) or NixOS.