This is not a particularly informative article but I see great value in owning a Twitter botnet. As one example, imagine negative news about a major public company starts trending. That would certainly be a money-making opportunity. There are also hard-to-disprove rumors that you could blackmail high profile people with. Celebrities probably don't want to be trending on Twitter for having an affair, even if it is a fake report.

So I am not at all surprised that people are investing in building up tons of what appear to be legit, active accounts.