Why do exes do this?

My ex broke up with me in October 2025. If she didn't end it, I was going to, both of us recognized it wasn't working. She asked for no contact and I happily agree, it's better to just walk away. I returned all her things. One month later, she texts thanking me again for the birthday present I gave her. Weird, but whatever. Fast forward to June 2026, she reaches out again to return a book. I said I don't care, keep the damn book. She insists on returning it. I say fine, drop it in the letter box. She insists on seeing me. Now she is asking to stay in contact but insists there is no way we are getting back together and thinks it might be unhealthy. But wants to message me occasionally. I don't want her back. Why won't she leave me alone? Why is she doing this?