Learning a new language _is_ easy for a good developers. I know of a lot of companies that are doing just that, trying to find good developers, and then train them on the fly in new language. And it works well for them.
The reason why some companies have "hiring problem" is that they require X years of experience with framework Y in language Z, although that language Z takes 1 month to master, and framework Y another two weeks.
Why are they doing it? Because HR is doing hiring, and because "hiring is problem" they get bigger budget for hiring, instead development department getting bigger budget for training.