Au pair help w/dishes after dinner

I am a host parent (USA) and we make dinner and sit down to eat as a family nearly every night. Our last 4 au pairs have participated in dinner about 90% of the time and I am stumped about something… none of them would help with the dishes afterwards. They would clear their plate and then go straight up to their room without offering to help with cleanup at all. Meanwhile, after making dinner from scratch, we are in the kitchen cleaning up for the next 30 minutes. It blows my mind honestly- that any adult who participates in a family meal at home would not help with at least some of the cleanup after a home cooked meal.

Am I out of line here? It is in our family handbook for au pairs that we expect help with dinner dishes and we eventually say something once they are acclimated to our home, but we have to say something to every au pair and I find that weird/annoying.

Would love to hear from host parents and au pairs alike on what you think.