I think the explanation for bimodal dev salaries is pretty clear, and is similar to the explanation for the bi-modality in Lawyer salaries. Google, Facebook, Amazon, and whatever other big name you want to throw in the pot, are competing for developers. However, they are not competing for the same developers as Epic Systems, for example. FAANG (or whatever) are competing for a highly skilled subset of devs that can m…
I think skill differentials in programming is a contributing factor to the bimodal distribution. I think there's also another factor which is the degree to which one is an active "curator" of one's own career. I've known some devs who were quite talented but were perfectly content to stay at low-paying jobs where the value they generated for their companies for developing CRUD or other low-multiplier apps was moderat…
Point being, there are probably lots of factors that combine to make a candidate skilled enough to get hired at Facemazon. It's just that having that combination of skills is rare, so the salary gap persists.