It's a consequence of Python never having been designed as a language with a static type system. In fact, Python is utterly dynamic and has a number of mechanisms that allow to write code which defies and mocks any attempts at static typing.

When the pain of maintaining larger codebases resulted in attempts to add static type checking (ultimately successful), it was, and still is, impossible to produce a solution that would work equally well for all kinds of codebases. Stricter tools show too many "false positives", laxer tools miss too many cases that a real static type checker would flag. Say, things that Django does (not to mention Zope) can only be described well by special-casing them. Hence different tools which strike different kinds of compromises.