New guys are expensive (especially in time), experienced guys are valuable.
If I spend a bunch of money/time on new guys I have less to spend on experienced guys compared to the company that just spends it on experienced guys. So, the companies that don’t train new can pay experienced more, thus getting the experienced guys.
That is the theory - in practice it is a bit different.
It takes a lot longer to become a senior who can easily switch business domains and tech stacks than it does to skill up in a single business domain and tech stack combo.
Two years in house is easily comparable with 5-6 years on the market if you work in a complex domain and have a good training program.
Our team is about 70% guys who learnt from scratch on the job I think. We have very low turnover, and you don’t come to us if you’re chasing max compensation anyway, so we do not have those problems as much (we don’t pay bad, but you can certainly make more other places).