Honestly, she's a pretty irrelevant personality. The Gamergate thing is part of it, but frankly most people who didn't like her probably didn't like her before that either. The whole issue is actually fairly well demonstrated by how you view her, as someone who doesn't know much about her but thinks she's well-liked. She isn't really relevant to most things, outside her having made a web series called "The Guild," aka "Super quirky geeks that are guildmates and take their guild/game too seriously while sucking at real life" the Show. Outside that, she's been an actress of varying levels of relevance in a decent amount of niche sci-fi shows.

Blizzard kinda latched on to her because of the Guild and the other geek connections and pushes her because of that. With The Guild, they started having her on Blizzcons for interviews back in ~09, and anecdotally I'll say that maybe one person in my 25-man 5-day-a-week raiding guild knew what The Guild even was then; we were mostly all confused as hell as to why this person was relevant enough to be interviewed when she came on. But in Blizzard's PR pushes they smartly shy away from trying to explain her too much because that creates the idea in people's heads if they don't know the interviewee that since Blizzard assuming you should know who this person is, they must be a pretty relevant and liked person. But this doesn't work as well with people who know who she is already and don't care or already don't like her and tends to cause them to resent her more than they would waste time doing otherwise.

Also, if you've paid much attention to Blizzard social media, they're a company that definitely latches onto the "Haha guys look at how GEEKY we are isn't this NERDY we're just total DORKS haha high five" sort of aesthetic. Like, if they'd developed Portal I'm sure that to this day we'd be seeing some reference to cakes being lies posted by their social media at least a couple times a week. A lot of people resent that sort of pandering for a variety of reasons that you could write a whole book on, but the character Felicia primarily plays, as per The Guild, is the "Look I'm quirky and SUCH a geek" character. As such, she kinda checks off a lot of boxes on people's "things I resent" list.

Personally, I fall in the camp of not really caring about her as an individual, but I definitely dislike the advert. I wouldn't ever go even as far as making a Reddit thread to complain about it, though it is obnoxious and is definitely something that makes me resent Blizzard and wish there was a way to communicate to them that everyone does in fact understand that they are geeky and that total geeks play their games. But, there are plenty of other things I'd like to say to Blizz first that are much more important than that....