That doesn't really make sense because most big accounts tweet about a range of topics. There's pretty well established ways for estimating the probability based on how the range of topics you might tweet about would match with the range of topics a user likes. That means you have to try and figure out what your base likes to see, and be like that. Tweeting about only a single topic means that you're only targeting people who are likely to like tweets from accounts that tweet about that one topic.