I haven't spoken to my ex in a year why did he block me all of a sudden?

I admit I check up on him here and there. We haven't been friends on social media for over a year and he has never cared to block me on instagram. He left me for another girl and he still didn't care to do it then or bother to hide anything from me.. It just kind of took me by surprise that he would do it now. When I don't try to talk to him or enter his life. What could possibly be the reason? Its unlikely that its his girlfriend. I was blocked then unblocked and blocked again within a week. Also fyi I don't want him back and I don't need to be told to not look at his page. I know I shouldn't care to make sense of it but honestly I can't help but want to. So any input is appreciated. thanks :)
I haven't spoken to my ex in a year why did he block me all of a sudden?
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