alt Hacker Newsits not large employers only. you need a steady stream and large enough pool of candidates for any size of a business.
if you limit yourself to a tiny almost invisible slice you are betting your business on finding candidates and relying on that small pool of talent. employees come and go and you would have to deal with this issue constantly.
Yes not only large employers, but it's easiest to think in those terms.
And it's only true that "employees come and go" is a problem if 1. you assume turnover has to be high, and 2. you don't know where to find qualified people you need. Turnover will be high if you assume you need commodity devs and don't, for instance, invest in their skills (like teaching them minority languages if that's your thing).
If I see a company hiring for "python developers" or "java developers" at this point I absolutely know what sort of problems their codebases will have, because they're in the commodity market and treating development as a cost centre to be minimised. Which leads to lower salaries, which drives higher turnover.
It's all self-fulfilling.