Lemmygrad isn't "hated" by most of the wider lemmyverse. There's just a loud and obnoxious minority of people that will rail and rant about lemmygrad. They loudly rant about lemmygrad because they aren't used to seeing their worldview get challenged and by its very nature as a radical leftist community, lemmygrad is a challenge to the typical background liberal perspective.
It's no surprise we all end up seeing a lot of threads about "those mean tankies at lemmygrad" (and hexbear too) made by people who can't take their worldview getting questioned, or even shown to be flawed, or just not standing up to their own scrutiny, and who get mad when that happens. There are also of course people with ideological reasons to demonize leftwing politics and will spread shit for that reason alone. But overall, I don't think most people care enough except to think "oh yeah that's that instance with those radical lefties, they're weird but they do make some great memes sometimes."