I won't argue that MS can't compete, but it's nigh impossible to migrate an entrenched audience. I wouldn't bother trying to create an alternative auction site to eBay, for example. All these things thrive on popularity, and a startup with zero followers (or single digit percentage sized market share) won't have the size necessary to attract the content to be something people want to adopt. Whether Facebook, YouTube, Twitch, Android, Windows, etc., there's literally no point trying to take these on unless one's willing to plough crazy money into forcing growth (eg. big payouts for users!).
There was one I was directed to recently, a crowdfunding startup just for indie games. Nice idea, but it's pointless if no-one follows it, and if no games use it (because there are no followers/users) then no one will use it so no games will bother releasing on it... Hence you have to use Kickstart or Indiegogo - an established player with the reach to actually work.