The difference is functions which return Result have explicitly chosen to return a Result because they can fail. Sure, it might not fail in the current implementation and/or configuration, but that could change later and you might not know until it causes problems. The type system is there to help you - why ignore it?

Because it would be a huge hassle to go into that library and write an alternate version that doesn't return a Result. So you're stuck with the type system being wrong in some way. You can add error-handling code upfront but it will be dead code at that point in time, which is also not good.