Why do people that hated you in HS expect a friendship later on?

I've received two friend requests on my FB from these girls that hated me in HS. One of them tried to turn my friends against me and the other spread a false rumor to others.
All of the sudden, they both greeted me with a ''Hey sup girl. How has it been?'' and ''Hey (my name) I was just stopping by to say hi to all those I graduated with. How are you doing?

Meanwhile I'm thinking ''wait a minute, we were never friends, why are you now acting like we're best buddies that haven't seen each other for years''. I haven't replied yet but I feel like sending that message. Why do people like them expect you to pretend nothing happened, expect you to be friends with them later on?
Why do people that hated you in HS expect a friendship later on?
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