Oh ya. This is the reason. I saw an article from Medium saying that they are doing some housekeeping--removing spam followers, sort of like to clean things up, so we will have a clean list of following. That's the reason. Wait... let me see if I can find that, I'll link at the bottom...

ok got it. Here you go--the link

https://blog.medium.com/keeping-medium-authentic-947feaf59415