Because it’s nice to reuse code. It’s virtually never the case that a function being compatible with too many types is an issue. The issue is sometimes that it isn’t clear what types will be compatible with a function, and people make mistakes.

Python’s type system is overall pretty weak, but with any static language at least one of the issues is that the type system can’t express all useful and safe constructs. This leads to poor code reuse and lots of boilerplate.