10 Reasons People Might Unfollow You on Twitter

You make too much noise! I eventually give up following people whose tweets take up my timeline and are constantly promoting themselves / products. A lot of affiliate marketers behave in this way and it’s considered spam.
Being boring
Making it all about you and not engaging with others
Tweeting offensive material
Begging for RT's
Being too automated
Too many DM's or automated DM's (my pet hate)
Hashtag overload
RT too many times and not contributing your own thoughts
Too political/religious