Sure, dynamic types are types. And nothing stops you from running a full-featured typechecker at runtime, one that can enforce useful invariants beyond “expected int but got string”.

It’s just markedly more useful to me to have that information available statically. I like being able to modify code with the assurance that the compiler will tell me about all inconsistencies. I like that the compiler can prove that its automated transformations are correct. Of course, maybe that says more about the way I work than type systems themselves.