Some people can change, the key thing being if they really want to, and they're internally motivated. You can't help someone into this state.
You have spent six years choosing to be in a relationship with a man who is incapable or unwilling, who cares which, of controlling his anger physcally and verbally.
Stop thinking of him as a cursed monster, that only your love and eternal tolerance will save, this is your ego. You need to feel like his saviour for some reason, spend your time and energy looking into that rather than why he is why he is, and psychoanalysing his childhood. Work out why you are happy to choose to spend your one precious life on this miserable dead end project, so you don't repeat it with the next fixer upper manshape that comes your way looking for your benevolence and healing love.
I'm sorry to break it to you my love, but you're not special, you don't have the magic touch, you can't "understand" him into being a better partner. You're no different to any of the other women on here who are absolutely baffled that they seem to have had children and are tethered forever to a mentally and emotionally deficient lump.
They don't change. He's got no motivation to change, if every time he loses his shit about a peice of Lego and throws a plate at the wall you're still there. If you don't think you're in an abusive relationship, then what is going on?
His parents may not have modelled healthy emotional regulation to him but that is NOT YOUR JOB, nor is it your burden to carry, your shit to deal with. End it, there is a life full of joy and peace and happiness and fun and love out there with your name on it, it doesn't need to be like this.