Why do ex's are mean after a breakup?

My ex broke up with me a month ago, I acepted the decision (even though it was hard) because the relationship was toxic : he kept on leaving, hesitating and coming back to me.

He had been very harsh during our break up conversation so I didn't try to reach him afterwards and tried to move on.

After a few days he blocked me on whatsapp, then after 2 weeks he unblocked me, waited a few hours and set a picture of a girl alone as his own profile picture. Then put a pic of him back. I have no idea who that girl is.
He probably expected me to go full psycho to test my feelings but I did nothing even thought I was choked and feeling terrible.

I know he did this to hurt me as he never posted any picture of us nowhere in 2 years and I had brought up the topic a lot at the time...

So my question : why does he want to hurt me if he's the one who broke up with me a zillion times and doesn't want a committed relationship? (this time it's over for real but still)
Updates:
11 mo
So my ex did this... WHY?
Why do ex's are mean after a breakup?
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