This mindset also creates and incentive for employers to keep their engineers from working on open source as much as possible, so that they don't look attractiv

This mindset also creates and incentive for employers to keep their engineers from working on open source as much as possible, so that they don't look attractive to other employers and are never able to jump ship / ask a pay raise. In general, I think it is a very lazy and ineffective answer to the "interviewing is hard" problem.