This has been a source of bugs since long before ChatGPT. I suspect Python tutorials mention it so often because it's such a surprising feature and causes so much confusion. I've been using Python for fifteen years, and it's the sort of thing that I'll still absent-mindedly forget if I'm not careful.

Ironically, in C++ - which does it the other way around - the tutorials mention that often because it is also such a surprising feature (i.e. people do not expect evaluation to occur every time there).

Thing is, there's no obviously correct behavior here, and there are valid arguments to be made either way. Which is why many languages dodge the bullet by only allowing for compile-time constants as defaults in that context (and if you want to evaluate something at runtime, you can always use an optional and do an explicit check inside the body, or provide an overload).