I have roughly a 1.5:1 ratio on Twitter, that being 1.5 followers for every person I follow. I gain new followers every week that unfollow me within 7 to 10 days. I'm sure some of them decide I'm not that interesting. They are probably right. However, I'm more sure that most of them unfollow me because I didn't follow them back. How do I know this? Those people almost always have over 10,000 followers, and are following a similar number themselves. Nobody can pay attention to a Twitter stream with 10,000 people in it. You just can't. So I know that person didn't follow me because they thought I might be interesting. They followed me so that I would follow them back. I don't play that game. Other reasons why I didn't follow you back include:
You didn't catch my interest. - If I don't know you personally or by reputation, I devote about 30 seconds to deciding if I'm going to follow you back. A Twitter profile that provides no interesting information about yourself is almost certain to result in me moving on quickly.
Your latest tweets weren't interesting. - If you aren't going to provide useful info in your profile, then it would be helpful if you at least had a few interesting tweets recently to give me an idea of what to expect. I err on on the side of opting out. You have to give me (and everybody else) a reason to care about what you have to say.
Your Twitter stream is mostly about self-promotion. - I don't really need to explain this one, do I?
Your Twitter stream is a late night rerun- If I've already seen 75% of the stuff in your Twitter stream, there isn't really much of a reason to follow you. This can be a particular problem with career related folks I've followed. We've all seen the that article about that thing by now. You don't need to retweet it. If most of your tweets are retweets that have hundreds of other retweets you might want to work harder at Twitter. Or just quit.
You appear to be a dick. - Don't be a dick.
Contrary to what the "personal branding" consultants tell you, nobody needs a Twitter account. It can be a great way to keep up on the news or an industry, but it's not a magic button. It won't automagically bring you sales, or fame, or influence. If you have fun with it, or gain something by using it even if you mostly consume content and don't produce any, that is fine. But don't feel compelled to participate. It's ok if you don't tweet. Odds are nobody is going to notice anyway.