It's a service that provides a convenient form of aggregation. It's not impossible to do things without one, but doing ad hoc peer-to-peer donations from a large number of donors to a large number of recipients in a very short amount of time is pretty difficult without some type of infrastructure to facilitate it. It doesn't have to be a general purpose donation platform, but whatever it is will have the same privacy factors I referenced already: independently of whether it accepts crypto, it will have to decide if/what user data to retain.