What's your evidence that Twitter's market is significantly larger?
Non-tech people sometimes ask me whether they should get on Twitter. I ask them why they might want it, and very often my answer is, "No, don't worry about it." And that's coming from somebody who uses Twitter enough to have two separate accounts plus a Twitter bot (sfships).
Twitter, like HN, is a niche social network. [1] Twitter's niche is much larger, of course. But I don't think it makes much sense to compare it to FB, whose target market is "anybody with friends or relatives".
[1] Technically, I'd call it a multi-niche network, in that it gets the most publicly active segment of people in a whole bunch of social groups. For example, tech people is has are the sort most likely to write books and articles, speak at/go to conferences, etc. But if you're the sort of workaday programmer who punches a clock at a bank and pays no attention to the industry, Twitter doesn't do much for you.