Why do people stop talking to you after you reject them?

I rejected one of my acquaintances because I’m in a relationship, but I’d still like to be friends and get to know her on a friend level. Ever since, she is cold and kinda avoids me in group settings (she’s also distanced herself from our friend group). Doesn’t respond to my comments on her IG stories. She eventually unfollowed me on all social media and removed me as a follower. When I tried to send her another friend request, she blocked me.
Why do people stop talking to you after you reject them?
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