Speaking for sorbet - no compilation step is a feature, not a bug. Imagine adding some kind of build step to every ruby app out there! Sorbet annotations are just valid ruby code you add to your files (you don't need to write separate type files - the sorbet system might do this for you though).

Sorbet also provides a gradual typing system where you can start adding types to a large code base and gradually make the checking more strict. Stripe claims to be using it on a huge ruby code base and that their developers generally like it.

However I think many devs don't want static types on Ruby. We like our duck typing!