I dunno if you're being deliberately obtuse, but just in case you really did miss his point: the fact that type hints are optional (and not especially popular) means many libraries don't have them. It's much more painful to use a library without type hints because you lose all of their many benefits.

This obviously isn't a problem in languages that require static types (Go, Rust, Java, etc..) and it isn't a problem with Typescript because static types are far more popular in JavaScript/Typescript land so it's fairly rare to run into a library that doesn't have them.

And yeah you can just not use the library at all but that's just ignoring the problem.