Product managers, especially technical ones, can bridge that gap without being too deep in either skillset. A PM, on the other hand, isn't expected to know all of the nuances and gotchas or frameworks of whatever language the devs are working in.

Devs will slowly learn the relevant knowledge anyway, just at a slower pace than the immediate needs. And yes, after a certain number of years, that dev could be good at both. But you can't only hire devs good in both places for every position at every company.