They can’t all be training there, surely. Covid regs. must come into play?

People get too set/cosy/stagnate when they stay somewhere too long, often without realising it, this could be a good move for him.

I don't understand the 'loyalty' comment, why is it loyal to stay in a decently paid job if you're not actively seeking to go elsewhere or indeed have any offers to go elsewhere? That's staying somewhere a long time out of necessity or not wanting to move from your job not loyalty.
Loyalty is staying when you have offers of other jobs that could enhance yourself/your financial position but elect to stay because you feel you can offer something and sacrifice the financial gain or are wanting to be kept even if the employer cannot match what's been offered.

Good luck to him.