...heh. The answer to all these questions (and more) is: "...because @leycec is lazy." Sometimes, it's not a virtue. 😢

In other words, @beartype currently only shallowly type-checks callables. Clearly, this is non-ideal. Clearly, however, deeply type-checking callables at runtime in the way that you and everybody else wants is super non-trivial. In theory, it's feasible for various subsets of pure-Python callables; in practice, it's rough stuff that we'd better think about very carefully before even attempting.

See also the official @beartype feature support matrix. Callable, for example, is still listed as "none" under full support – meaning that @beartype currently only shallowly type-checks callables. Pour one out for @beartype. 😭

Yay! So sorry about that, @Artur-Galstyan. And thanks for sticking it out with @beartype despite API growing pains like this. 😞

Proper Callable[...] type-checking is definitely on the roster for an upcoming release – but leaning towards the end of the year now. The future is so bright I can barely see it.