There is a slang term Karen that applies here.

Our school definitely doesn’t assume everyone
One year our school scheduled a professional day with a month’s notice! I guess it was on the internal calendar but not the parent one. That was insanity but we all pitched in to cover for each other and complained for a few minutes about the lack of notice. No amount of complaining would have changed reality and I think most parents realized that.

Sometimes things happen and it doesn’t mean anyone’s out to get you.

According to OP, this event was tentatively on the school calendar since the fall for this date, and the reason for change is that other pre-scheduled events also fell on that day - not an emergency or late breaking change in circumstance. Late notice for the change is annoying in that case because the late decision wasn't necessary. The school knew since the fall that it would have to confirm the date to parents and had plenty of time to do so with more notice.

In different cases, as PPs noted, two weeks notice would not be feasible.

FWIW, I do not think schools, at least the ones I'm familiar with, assume kids all have SAHMs.