Investment, too. Investors want to see activity, and you're better off showing useless activity than none.

Plus, you don't grow to a tech behemoth (Google, Microsoft, Facebook, et c.) by running smart & lean. You might get bought by them that way (cf. WhatsApp, and maybe even Minecraft) but you don't become one of them. So if leadership/investors thought Twitter had a shot at joining the big-boy club, maybe that's why.