I tried to brainstorm what they might be thinking.

• MIRI is making a mistake that means its' work is useless
• MIRI won't decrease AI risk unless some other intervention is done first (there is a rerequisite)
• We're doomed, resistance is futile
• Other people wll fund it if they wait (seems unlikely, if the amount required is trivial to them)
• They have political/strategic reasons not to be associated with MIRI (if they contribute anonymously, there's still the risk that other donors will disappear and they'll be stuck supporting it indefinitely)
• They'd rather work on the probem wiht their own organization, because of reasons