RMS wasn't "cancelled" (a reminder that "canceling" and "canceled" is a snarl word.)
His decades of incredibly shitty behavior came to be more public knowledge as both men and women in CS realized the behavior they'd witnessed wasn't some outlier once a few women who were well-known came forward and disclosed his behavior.
What brought it all to bear was him repeatedly, on a technical mailing lists, defending sex with underage girls, which in turn led people to actually go looking through material on his own site where he pontificated that sex with anyone over 14 should be legal, or even younger. These are his exact own words:
"I think that everyone age 14 or above ought to take part in sex, though not indiscriminately. (Some people are ready earlier.)"
"I am skeptical of the claim that voluntarily [sic] pedophilia harms children. The arguments that it causes harm seem to be based on cases which aren't voluntary, which are then stretched by parents who are horrified by the idea that their little baby is maturing."
Add onto that decades of stories of creepy, manipulating, harassing behavior toward girls/women as well as incredibly sexist comments about women's technical abilities...among a lot of other really anti-social behavior, like an apparent refusal to bathe...while expecting anyone who hosts him to read a 40 page long missive about exactly how treat him.