Here's what I don't understand. How are scientific projects constantly having funding crises? The set of people who are most interested in seeing Kepler, JWST,

Here's what I don't understand. How are scientific projects constantly having funding crises? The set of people who are most interested in seeing Kepler, JWST, etc. succeed strongly overlaps the set of people who have the sort of money needed to make these projects be successful without even significantly impacting their life style. Asking as a stereotypically poor college student - why do these projects not have nontrivial amounts of "private" (not for-profit, just "private") funding?