(edit - quoted wrong post, meant to quote you asking what abusive men get out of it)
The best explanation I have ever read is in a book that's often recommended here, "Why does he do that" by Lundy Bancroft. You can download it for free online - just Google it and you'll find the website. It's honestly a total eye opener that makes so much sense, written by a man who spent his career working with abusive men and their victims. The point that really struck me in the book was that - it's not about feelings, it's about thoughts. We so often fall into the trap of thinking "oh, he just has such big feelings, he just needs to channel them more appropriately", when actually it's his underlying beliefs which cause the problem - beliefs which boil down to a sense of entitlement to control. Once you've seen it, you can't unsee it.
E.g. imagine you were upset because you thought your boyfriend was getting up to things you didn't approve of with his friends, and on his computer. You might be upset, angry, you might leave him. What you probably wouldn't do is feel entitled to film his friends or ransack his PC deleting his files. An abuser thinks they are entitled to do anything if they consider that you have slighted them. They might not even have the self-awareness to realise that's not normal. I have heard men say things like "Well, she did X, so of course I did Y" or "Well, his girlfriend did X, so of course he did Y" - not necessarily instances of abuse per se - and I'm just sitting there open-jawed thinking "WTF? Why "of course"?! That's nuts!". These are men who otherwise may seem/be perfectly pleasant and reasonable, but have a massive blind spot regarding what it means to respect another person. At the extreme end of the scale, you will read about men in the news who feel justified in having killed their wife because she did something "wrong".
I don't think most abusive men think "Hee hee, first I'll pretend to be nice, then bam! After six months, I'll start being nasty!". They just don't respect other people, especially women, as autonomous beings, and they feel entitled to use any means necessary to control or have vengeance on those who bruise their egos. They have also learnt that they need to lay on the charm in order to form the initial relationship.
Look up covert narcissism as well. I know the word narcissism gets thrown around a lot, but reading about covert narcissistic is helpful in making sense of men who seem sweet and humble, yet also have a dark side that lashes out.