Companies tend to be way too specific about the skills required and any learning curve is not permitted. I've used just about every desktop UI framework under the sun and a whole bunch of web ones, but companies that need react developers won't look at me for instance. There might be some highly specialized skills that can command a premium but those are mostly rare exceptions.
Along with companies not training there's also been a shift away from specialized roles and requiring all devs be experts in every tech the company uses past, present and future. When they hire someone that knows x "just in case" they're shrinking the talent pool available.