You may not have known that they had a tattoo, but that is very different from them not having them.
Aircrew know the rules before we join up. We tend to be quite driven and informed. Young lads and lasses are less so.
I think this is a legacy of cold war warriors. Back then image maybe was more important. The last few years of conflict have perhaps focussed minds on rather more important metrics than whether they look good in uniform?
We currently have trouble recruiting either the numbers or quality of people we want. If you want to filter, filter for reasons that actually impact effectiveness, not visual impact.
Plenty of RAF aircrew with tattoos and even piercings.
The outside world has come to terms with tattoos long ago. Not a fan myself, but my brother is very high up in one of the big accountancy firms and he is covered in horrible ink and piercings. You know what, nobody cares because he is good at his job.