https://en.wikipedia.org/wiki/Boys'_love_fandom has been the best explanatory media that ive seen , but the best explanation i can also give is that fujoshi started as a misogynistic and homophobic term , fujoshi quite litterally translating into "rotten girl" as it was meant to call women "rotten" for enjoying bl / yaoi , a good bit of people nowdays seem to be going back to the misogynistic meaning it seems, while some critical views against fujoshis are valid (ie some of the fetishization i see from some fujos, though i dont consider those as actual fujos) most of it tends to be misogny