[Question] “Fanatical” Longtermists: Why is Pascal’s Wager wrong?

I’ve recently heard a number of people arguing for “fanaticism“ when it comes to longtermism. Basically, if a cause area has even a minuscule probability of positively affecting the long-term future of humanity (and thus influencing an effectively unbounded number of lives), we should fund/​support that cause even at the expense of near-term projects with high probability of success. If this is so, I have trouble seeing why Pascal’s Wager (or the even less probable Pascal’s Mugging) shouldn’t hold. I know most people (even religious people) don’t believe Pascal’s argument is valid, but most arguments against it I’ve read would seem to also exclude low-probability longtermist causes from being valid. What am I missing here?