What you really want is the Jeet Kune Do guy, who has tried a bunch of things and is good at learning whatever he sets his mind to. You've all met him, that guy

What you really want is the Jeet Kune Do guy, who has tried a bunch of things and is good at learning whatever he sets his mind to. You've all met him, that guy who's never written a mobile app and then when it crosses his mind, a few weeks later he's written a Swift app that talks to APNS and all that. A colleague of mine went from his PhD in Biology to writing low latency c++ HFT code. The problem is we all like to kid ourselves that we're that guy, and we'd like to kid other people (hiring managers) as well. So to guard against this, the natural thing to do is to restrict the entry criteria. I'm not saying you won't turn away any genuinely great people who can learn your system super fast, just that in this case the baby/bathwater ratio seem pretty reasonable, and so that's why people do it. I would think that in a tight job market like we have now, the criteria are a bit looser, so it's not all bad.