You didn't mention my sole reason for donating to multiple charities: I consider some of them obligations. For example, if I benefit from a service or have in the past, I consider that I owe it to the ongoing enterprise/community to support it in turn. But once those are satisfied, then it's Givewell's top pick for the serious money.

Even a dyed-in-the-wool consequentialist could reason similarly, given Viliam_Bur's point about encouraging others to donate. Considering certain things "obligatory" can have good consequences like that. But for me, no such indirect route is needed.