Most are themselves, very hateful individuals. It was something that the previous iterations mods had to bring up many times. I guess the simplest explanation is that it makes them feel good about themselves. We are an easy target, societal rejects, and there are no repercussions whatsoever in this world for mocking, bullying or often assaulting reject men who aren't considered to have value by the rest of society. This presents itself as a prime opportunity to hate others and feel justified while doing so. Poor rationalizations will be made, hypocrisy, gaslighting, sweeping generalizations, ignorance and attempts to redefine terms to name a few things all in the effort to reinforce and enable their own hatred. Typical of most people who harbor hatred for groups of people they don't fully understand. The same way bigots operate honestly. But like I said, there are no repercussions.
Normal people certainly don't care, they however don't turn their bullying of us and hostility towards us throughout life into an online sport. The simple reason is that it makes them feel good. It gives them an ego boost, not only to feel superior to us, but many people enjoy how hate makes them feel in general. The idea that they're fighting some "noble cause" allows them to inject a sense of purpose and self-importance into the mix too. You'll see them chase this fix a lot through erroneous means. Often by posting content that has nothing to do with incels, falling for obvious bait, all the way to quite literally creating their own false flag content.
Honestly, for most of them you only need look through their account history to find out that they're often not very empathetic people and have a whole bunch of hate bottled up inside them. That said, not all users there are hateful. Many just fell into the trap of thinking all incels are bad people and all exhibit X trait and all think the same on everything etc. Which of course is probably an easy mode of thought to fall into when thats all a lot of media/subs say. Very few people are writing articles about why this isn't the case simply because it doesn't fit the general narrative of outcasts, they've made no attempt to actually look into the issue deeper with an open mind, and ngl its not "juicy" enough to talk about reject men if there's no controversy to be had. People discount and ignore incels who aren't saying anything provocative. So far there are only a few non-incel people creating content, or researchers conducting honest research that isn't intended to demonize us. But you often find these people have actually approached this whole thing without bias, without their own hatred, and the ability to somehow consider us to be human beings.