Why do people (Mainly girls) block their ex soon as they break up?

So you have a 3-year relationship, with its ups and downs. Things get a bit bad (Arguments) not insulting etc. But overall the relationship was good and has so many good memories. Either way, you decide to break up. To the dumpers specifically, why do you then go blocking them from everywhere like they are enemies and that the 3 years didn't have any meaning?
Why do people (Mainly girls) block their ex soon as they break up?
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