I think part of it is because you have a lot of new comers that Spam you with following, only because they want you to follow them back for numbers. They aren't necessarily following you because they like what you write or plan to read what you write. They just follow you in hopes that you will follow them.
That can be offensive to some. People don't necessarily want you to follow them to try to increase their numbers too, they want to be followed because they are good writers and actually write things that their followers enjoy.