It may be to encourage 100% participation (none of our schools did this but I know it exists). But more likely it's polite, so as to not make a family feel bad if they hear about the parties. And because fundraising is about casting a wide net. You just never know.

My friend is on very questionable FA and I can totally see her and her husband making a giving level donation so they can attend the high roller cocktail parties and cement their outward rich person status - while on FA at multiple schools. Yuck.