>There are no infinite rewards in biology and yet mathematicians seem to do just fine answering these sorts of questions

This is only a problem if you're already assuming we do everything based on our biological reward systems, and in the current context that would be circular reasoning.

Imagine the treasury creates a "superdollar", a product which, if you have one, you can use to create any number of dollars you want, whenever you want, as many times as you want. Obviously a superdollar is more valuable than any finite number of dollars, and humans/mathematicians/AGIs would treat it accordingly, regardless of the finiteness of our biological reward systems.