I've hired tons of developers with 15+ years of experience! A lot of them have amazing OSS contributions. Some don't but all can talk in depth about projects they've delivered.

Hiring based on open source contribution isn't the only signal one can look at, it's just a very strong one (the strongest in my experience).

I'll add that not all developers with 15+ years of experience can ship software. Many have let their skills deteriorate or never pushed themselves to learn new things. It's yet another reason a strong personal portfolio is a good signal.