Many such geniuses (top intellectual performers in fields where they can out-perform the median by several orders of magnitude) choose their work not just on the basis of payment, but what they work on, where, how, and with whom (preferring the company of other top performers).

If MIRI were to compete with Google at hiring programmers, I expect money be important but not overwhelmingly so. Google let you work with many other top people in your field, develop and use cool new tech, have big resources for your projects, and provides many non-monetary workplace benefits. MIRI lets you contribute to existential risk reduction, work with rationalists, etc.