That's because it's not about 'punishment' or 'reform' for the targets, the Cancellers could not care less about any actually productive change being induced. They just want someone to beat on and harass. If we lived in some kind of sick society that, by lottery every day, picked out one person to be a pariah to jeer at, humiliate, and get gang-beaten to death, it would be these Cancellers that would be first in line to stomp on that daily pariah, because they just want a target that they can sadistically torture without consequence. The Cancellers are scum, the "Culture" is just a facade.
I don't think it's as easy as just malice. I've pointed to witch-hunt mentality mechanics before. In my opinion, it's very tied to virtue signalling – yes, I know I am doubling the buzz word quota of the discussion but please bear with me: virtue signalling is used as a social tool to signal that you are virtuous (duh), but also, it is another way to signal that you are part of an in-group and soecifically that you are worthy of being part of it. Classic examples of virtue signalling that everyone in the west can relate to is the old-timey image of Dickensian upper class people who go to church every week and sit at the front so that everyone can see them and then ignore the impoverished begging for alms as they leave, I'm going to use this contrast with what happens today because there's a big difference in the social mechanics here stemming from how on the Internet, you only exist if you're making noise. This causes virtue signalling to change from something passive into something that needs to be actively pursued.
Then, we have a very large population of people who are, as it had been dubbed, chronically online. These are people who have very limited interactions with people in the "real", offline world. Their contacts and communities are more or less entirely online-based. When coupled with the "exist only if you're seen" mechanic, this means that it's very hard to passively belong to an Internet community, and it's very hard to signal your virtues to it, because the realspace world and offline actions does not exist in the online world. You can't virtue signal by sitting at the front of the "online church", because everyone else in the "online church" are only seeing the "priest at the altar", the centre of attention, that is whatever hashtag is headlining twitter at the moment. But the feeling of wanting to feel like you belong to a community is just as strong in "chronically online" people as in others, the difficulty of feeling like so just makes the need to feel it stronger, and they chase harder to get it. To be seen as being part of the group you have to move yourself from the silent church goer crowd to being the priest.
This is where "witch hunt" mechanics enters the picture. A witch hunt, socially speaking, is just not a drive against a single target. It is also a way for people to signal how they are better than the target (more "virtuous"). But it's not easy to prove that you aren't a witch. You can say "I'm not a witch" but that's just what a witch would say – in fact any attempt at defending yourself against being called a witch, both preemptively or after an accusation, during a witch hunt will have the effect of making you seem more suspect and more accusable (even just defending somebody else under accusation will mark you as a witch). Socially, the only way you can show that you aren't a witch is by accusing somebody else of being a witch, preferabbly before the accusation is levelled at you. This means that during a witch hunt the only way to prove that you belong in the non-witch group is to join in behind the first accusations as soon as possible, the only way to signal your virtues is by attacking the unvirtous.
So all in all, we have:
1) An Internet where you only exist if you are being heard (I'd say this actually extends to our societies' media environment in general, but it's especially so on social media)
2) People who because of their lack of connection to realspace communities have a strong social need to prove themselves as being part of intangible Internet communities
3) The mechanics of the witch hunt meaning that as soon as a target is identified, social interaction devolves into a game of bullying and ostracition.
And when these are mixed together, you get a perfect storm. 3) mixed with 2) means that people have an increasingly strong need to prove their non-witchness to the group to feel that they belong in it, making them more likely to engage in the hateful "always attack" mechanics without pausing to think "is this a proportionate or reasonable response", and the addition of 1) means that your belonging only exist for as long as you are trending, and you have to keep making yourself heard to be part of the group. This means that not only are people going to be more willing to extend and go further during a witch hunt, they will also be more prone to seizing the opportunities to start witch hunts in the first place.
Outrage culture ("Three! Three buzz word terms! Ah-ah-aah!") is also strongly connected, I guess
In the end, it's the result of people becoming more and more isolated and having a lack of real connections to real people in realspace. But I know you folks probably don't agree with me about the terribleness of Internet, computers, and digitalisation of society.