I think the more reasonable explanation is that there actually are hundreds of independent entities sending this sort of political spam.
This stuff must be effective or else they wouldn't do it. On the other hand, it seems like a good way to discourage repeat donors. Why would I donate any money if the result is going to be endless texts and emails?
Heck, maybe they should offer a "premium donation" where you pay extra to not get on these lists, analogous to a no-ads streaming plan.