I would MUCH rather hire someone who is a quick learner and can adapt and figure things out (which in my opinion, is the sign of true intelligence -- "problem solving") rather than someone who is knowledgable in a niche area. Granted, there are exceptions, and if someone is designing a nuclear reactor, you can bet you want someone who is an expert at that one thing. But generally speaking, I think polymath abilities are much more useful.
For a manager, running a project is about combining resources and getting a product in the end. So they get X developers with N years experience in `foo` and `baz`, allocate M months of salary and collect the product in the end. If you "don't know, but can learn", you don't even get hired, they cannot justify paying you a salary to learn.
I'm sure this is different in certain circles (SV, other startup hubs), where you have companies led by engineers or with an engineering mindset, but that's how the song goes for probably 90% of the world's IT industry.
My coding beginning was actually when I started a business picking up dog poop (no joke) when I was 9 years old to buy an N64. I convinced my dad that I needed a website if I was going to be a "real" business, and he taught me my first HTML.
