I think it's because you don't maintain much python code, or use many third party libraries.

An easy way to prove that this is the norm is to take some existing code you have now, and update to the latest versions your dependencies are using, and watch everything break. You don't see a problem because those dependencies are using pinned/very restricted versions, to hide the frequency of the problem from you. You'll also see that, in their issue trackers, they've closed all sorts of version related bugs.