Why are some people like this?

I make friends online. I talk to some of them for years, and some of them stop responding to messages after a while. I had made a few close friends in particular. I don't even have such close friends in my real life, but unfortunately these friends haven't been replying my messages for months or even years. Our communication has officially stopped. Why are they doing this? Even though I didn't know them in real life, I felt very close to them. They had become my confidants😔😔
Why are some people like this?
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