Why do people hate Kaisagi so much?

I just don't get why it gets a lot of hate in general. When I read the manga, I instantly liked the pair because they just have so much chemistry. I went to twitter to find content but I saw a lot of blk fans hating on the ship and its shippers. Sure they used to hate each other's guts, but is that reason really enough to hate the pairing and the people enjoying them?