My personal anecdotal experience is considerably different. I've worked multiple places where I had to learn the stack on the job. Up to and including the language at least once.
I've never found it too difficult to get hired even when the requirements don't list something I've done already.
You’ve been lucky then, or have excellent credentials, or some combination of the two. Your anecdote doesn’t invalidate their point about it being a valid reason a dev would want to gain experience in a current and modern technology over an archaic one.
I've never found it too difficult to get hired even when the requirements don't list something I've done already.