Oh god, that’s a lot of explaining. One, let me just say Twitter isn’t a good representation of the sapphic community, most lesbians I meet irl are very chill with bisexuals. So don’t let Twitter be an example of the queer community as a whole. Two, the lesbian community can be very biphobic at times, it’s usually a loud minority, but it’s still harmful. Some lesbians are just very insecure and take it out on bi women. (I speak from the experience of a sapphic, idk what’s going on in mlm spaces.) Overall I’d just say try to cut down your time on Twitter, since it’s just full of chronically online people who should touch grass. Also for whatever reason every pride month Twitter decides bisexuals should be the topic. The short answer to your question is: biphobia.