Vet tech here. If the one with hygiene issues is overweight (no judgement!) it could be they just can’t reach. Or if older, could be arthritis makes it painful to groom.
If young and skinny and it’s always been that way and otherwise healthy then it’s just a mindset maybe 😉
Know the feeling. I have one cat that spends 30 minutes covering up some business in the litter box and another one who clearly does not not feel the need to be bothered.
You have made a common mistake regarding cats and ownership. You do not have two cats. Those cats have you. My best advice is do not try to understand, just serve.
