Why do internet marketers on Twitter only unfollow people who aren't following back?

[Pete]

Wouldn't it make more sense to just gradually unfollow everyone? So then you can follow even more people (because there is a limit to how many you can follow at once)?

I mean it's not like people will unfollow you just because they see you unfollow them. Or will they? Do they get some sort of big notification that you unfollowed them? Does it make them unfollow you automatically? What incentive do marketers have to only unfollow the people who aren't following back?

[TwitterHelpCat]

They are probably using and automated twitter bot that unfollows people after a certain amount of time if they don't follow back