Why do some subs just go 100-0

So for context, I used to be a sub in this and saw the same phenomenon back then when I used to talk to my domme friends. Now that I'm on the other side I have experienced it first hand.

Subs would reach out to you all excited and wanting to enter a dynamic, you talk a little and all of the suddenly they up and vanish, some event deleted their profiles on me. I thought we were making headway but I'm just baffled, why not just say goodbye or something, it's really bizarre. Any input on this from either side as to why this is so prominent?