When i read your opening post i thought "shit! that sounds like my sis!". Having read the whole thread i can see that he IS my sister but in a mans body!
The way to deal with his bullshit is by being blunt, matter of fact and placing the responsibility of fixing the situation back on to him. TELL him that you don't believe it was 'accident' or 'thoughtless', that you hold him responsible for destroying your possessions - and what is he going to do to replace them?
From my own exp with my sis i can tell you that this is all calculated, premeditated, passive aggressive CONTROLLING behaviour. When they eventually get called out on it they do all they can to minimise it and turn it back round on you. All of which he has done.
He's feeling confident that you will react the same as you did every other time he violated your trust and destroyed your possessions - and i suspect you are. You already sound 'defeated', as though you've 'accepted' this latest episode - and that is exactly what he is counting on. If you won't stand up for yourself then this will only be repeated in the future - because you already know deep down that you can't/don't trust him anymore.
The 'why' bit - some people are just nasty and mean that way, could likely an issue or hang up from childhood that has followed him - but that still doesn't EXCUSE his actions. He did this to deliberately punish you - please don't forget or minimise that. Just like my sis, he has no problems accusing others of 'hoarding' and being 'dysfunctional' but the minute you accuse them of having issues suddenly it's all 'psychobabble'.
Exactly like my sis, he is deliberately walking all over you but making sure that he can't be held responsible for any of it - by using 'didn't think' as an excuse and by turning it back round on you for 'hoarding silly things'. When you do stand up to him he gaslights you, lies to you and makes you feel like you're 'blowing things out of proportion'.
I couldn't remain in a relationship with a man who behaved like this. My sis picked a spineless manchild who doesn't stand up for himself, his kids or even his own family in the face of my sis's games and nastiness. People like them pick their 'victims' carefully and they only show you their 'true' nature once they believe they've got you backed into a corner...