The dopamine drip from the little bell lighting up to let you know "retardfucker69 liked your post" was taken away, which is what everyone is seething about itt.
All of the reasons people have given for why they want sticker notifications still exist, you can go to your reactions received page if you want to see who is reacting to your content, there is a watched thread section, threads with your posts section, reply notifications, all things which accomplish what everyone here says they used sticker notifications for.
The real reason is people aren't getting the serotonins from the little bell lighting up everytime someone clicks "like". At least a couple people have the decency to be honest about that.
The funny thing is I don't even disagree that the option shouldn't have been taken away, but the sheer amount of seething this has generated makes me hope the autists here suffer eternally from sticker deprivation.