If you're concerned as to why your Twitter following is slowly dissipating than perhaps the Unfollow on Twitter Infographic can provide some valuable insight regarding your diminishing online popularity.
According to the chart, 52% of people stop following a Twitter user because they are too noisy. A clever or funny personal tweet here and there is always appreciated, links to interesting news and developments are a great way to spread the word, but after the 10th tweet of the day concerning one's dietary preferences or pet peeves it may be time to move on.
Other reasons why people lose Twitter followings is because of too much self-promotion, too much spam, not interesting enough (ouch) and too much repetition. Twitter gives people a great opportunity to share witty and relevant information, those who abuse it will see their beloved following drift away in light of "hashtag abusing."