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The answer is that some people do quit and retire early, but even more are attracted to that career like moths to a flame, and work until they can't.
I do think they should raise pay for their existing employees at the same time. In fact, they should tie the compensation to progression in skill and experience, so that people who just came for the money and aren't cut out for the work or aren't in it for the long haul aren't attracted to the job. That's basically the traditional model anyway.
And yeah paying employees well might cost a bit of money (but really, not that much in the scope of things). If talent is their production bottleneck, it will be well worth the expense.