The Sea Wasp (Ryk E. Spoor)

In the end, they do it because it works. There are always enough hard core supporters who will respond every time, and it costs them more to sort out who is who than to just spam everyone.

As a side note, no charity associated with the police or fire department will ever call you soliciting donations. Ever. They make a point of not doing so because of all the scams in their names. If you get a call from someone claiming to be collecting for a police or fire related charity, report them to the real police.