Fandoms are a powerful thing and people develop an attachment to their favorite characters. Varus's lore did change him quite alot, so it's understandable why all of the Varus mains and people who loved him might have been upset over the changes. Old Varus wasn't boring or lifeless, he just had a different approach to essentially the same theme and story (Village gets invaded and lover gets killed, in order to get revenge he allows himself to become corrupted). You have to realize though that it's the little details that shape a character. I personally enjoyed both his old and new lore, though I completely understand why many are against the new one.
Also I've noticed how both sides of the argument seem to enjoy undermining each other's preferred lore, saying things like "the old lore was lifeless, man's family dies and now he seeks revenge, how generic," versus "the new lore is so dull, two gay lovers get taken over by a darkin, the old lore was better." Those that liked the old lore better think the new one is more dull, while those who like the newer better think the old one was dull. It's clear that everyone sees shit differently.