Probably because its too much - I struggle to accept donations on my project as well, especially when theyre larger than price-of-a-coffee.
So I only accept substantial donations if I'm very sure I'm going to be able to do a substantial amount of work on the project going forward.
The sender didn't reply to messages.
I really wasn't sure what to do. And without a document saying it was a gift from the sender, I had to give half away as taxes, and then there was no possibility of returning it (I wouldn't be able to reclaim the taxes).