The reason: iOS 5. Apple introduced iOS 5 on October 12th, and with it, a host of new features. One feature in particular is the backbone of this article: Twitter integration. Tweeting is now possible straight from the native apps Safari, Photos, YouTube, and even Maps. All one needs to do is click the button that brings up extra options in those apps (i.e. Bookmarks, Print, E-mail, etc.) and boom there it is, the new "Tweet" option. This is Twitter's 50 caliber sniper: came out loud, may only take the competition down slowly, but eventually it's going to cause a lot of damage.
The popularity of iOS gives its apps and developers an uncanny ability to become a dominant player in the mobile business. Games and apps like Angry Birds and Yelp are perfect examples of this. Therefore, needless to say, being natively integrated into iOS must be nothing but great for a company, which is why Twitter has found it's Holy Grail. Google and Apple have been at odds for a while so it's no wonder why Google+ was not the social network of choice, and maybe Facebook's friendliness with Microsoft had something to do with why it was not chosen. I haven't seen any concrete reasons on the latter yet, which to me is the more important of the two.
Having Twitter integrated into iOS exposes it to a large user base, many of whom are social media enthusiasts. However, as we all know, most social media users are kings and queens of the Facebook world, and only travelers or vacationers to the Twitter scene. iOS will likely change this, or at least change the amount of traffic through Twitter. I think that many people will connect their accounts so that when they update Twitter it will also update their Facebook. I think that the privacy and ease of placing people in groups ("Lists") available through Twitter will also help steal users from Facebook once people become more accustomed to it thanks to iOS.
Written by: Andy
Pictures: I'm Bringing Blogging Back and Sense iPhone