Additionally Twitter has as far as I can tell (speculative) a much much less stable foundation in the EU then it seems if you just look at daily users count.
iMessage? (US)
WhatsApp? (EU)
EDIT: It's not only what everyone has (WeChat in China), instead of just many people (WhatsApp in EU). It's also the default payment service, you pay through it all the time in all kinds of situations. It's like WhatsApp but more monopolistic combined with PayPal but also more monopolistic. And both with full government support so no worries some bank lobby gets in you way.
If he has ambitions to turn Twitter into an Everything App, he'll need to diverrt a significant portion of the workforce onto that project, leaving him with a fraction of a fraction of the current workforce to keep Twitter's microblogging and ad shilling platform up and running.
If not even Facebook with its userbase of people already using a single mediocre tool for different purposes manages to crack the "everything app for the west" nut, Twitter is bound to fail.
Maybe everyone is bound to fail simply because the concept does not fly in the west.