The trolls failed to sink Captain Marvel earlier this year, so they are targeting Batwoman for now, until something else comes along to attack (the next Star Wars? Stargirl? Ms. Marvel? Mighty Thor? Who knows).
Many don't read the comics and know of Batman from other media, so they can't tell the difference between Batwoman and Batgirl (or Catwoman apparently), and are too lazy to look it up. And since Batwoman, unlike Batgirl, is very new to media outside of the comics, most non-comic fans will assume she is Batgirl and have jumped to the conclusion that she was re-written as a lesbian by the CW.
Mind you, if it was a Batgirl show, it would still be getting review bombed for being a female lead and the absence of Batman, but likely a bit less 'cos Babs is straight.
That, and the actress seems to have a swarm of dedicated haters (and judging by the comments they leave on articles about her etc, most are also based on misogyny and homophobia, whilst some others attack her for being a "fake lesbian" as they put it).
Actually, if you remember back to the casting controversy, many of the twitter haters attacked her for stuff like "not being lesbian enough", "a lesbian that appeals to straight people", or being "too pretty". A different species of troll, but also trolls who just have it out for the actress.
https://www.advocate.com/arts-entert...-rose-batwoman