The donor has said/intimated they they have enough money from bitcoin that they own that they really dont need the rest and so it may as well go to good causes.

The donor has said/intimated they they have enough money from bitcoin that they own that they really dont need the rest and so it may as well go to good causes. He/She/They can probably expect something of a tax write-off but I imagine that taxes arent really a problem for them either. If you are happy to give away ~$80m then paying ~$10-20m in taxes is not going to phase you.