My in-laws visit for a couple of nights every few weeks, and I don't always wash the bedding in-between.
I know my MiL has a thing about this because she once criticised (to me) her other son's wife for the same thing when they had kids and we didn't. Also, on the day of leaving she always asks me if I would like her to strip the bed, even though I always say "no thankyou", whether I plan to wash the bedding or not, because I don't want to feel pressurised into doing it immediately.
AIBU? I don't think so. I just wanted to sound off because I find it frustrating.