I suppose, in defence of the cabin staff, if you're confronted with a bunch of 18 - 30s who have decided they aren't going to comply, when some of whom may well have been inebriated what choices do they have? Probably the only sanction worth threatening them with would be diverting and kicking them off, but financially times are hard for airlines, and it matters not how many country court judgements they might get against the offenders, the extra cost of a diversion is never going to be recovered.
Incidentally, there are no "very good excuses" for not wearing a mask; you knew the rules when you booked and if you feel you can't wear one, then you shouldn't have booked. And similarly, if you have a true medical condition that means you can't wear a mask, then don't fly. Simple!