University research is labor. Researchers get salary or stipend, usually relatively modest on the ridiculous white collar standards. Nobody gets rich from grants. Typical best case scenario for grant researchers is to stay employed. Tenured faculty don't get any money from the grants.

(Very) few do get rich by leeching publicly funded research for spin-off companies. High level admins can get relatively rich from obscene salaries, but they aren't the ones applying for the grants or doing the research.

Probably not altruistic, but not usually primarily for money either. If money is what you want, university is a very bad place for trying to get it. People do do things for other reasons than economic gain regardless of what the prevailing economics dogma and ideology claims.

Nobody gets access to the money privately. The grant is paid out in salaries for work instead of capital gains. There's no capital investment for the grant.

Of course grants are an economic incentive to do something. But not all economic incentives are profit.

Edit: To be clear, universities as such don't generally apply for research grants. Researchers in universities do, and for getting a grant they get the luxury of working for a salary for a few years, or getting somebody else to be paid for their work. Universities do take a cut (overheads) from the grants to nominally pay for infra and admin etc, but in reality a lot of it is spent on all kinds of non-related things like teaching and alumni dinners and chauffeurs for the provost.