That's the first thing that came to mind. It's a pay-to-play move, which is not at all surprising. People seem to forget that fully-featured social media-centric corporations are run for profit, and if they can't get enough advertising to balance the books, then what's left but subscriptions?
Sometimes people buy media corporations because they're interesting in using them to promote their other more lucrative operations (think Jeff Bezos and the Washington Post) so they don't really care about profitability, but I don't think Twitter fits that model, but who knows?