You can do some pretty extreme things with Swift. I'm not talking about the kinds of apps you can create, I mean what you can do to the language itself. For example, you can change the meaning of the equal sign for any class you choose. This may sound crazy, but you will hear more about it in my upcoming meetup event on May 5, 2015 at WeWork Chinatown.
You will find that many features of Swift exist in or were "stolen" from other programming languages, but comparison is pointless for all practical purposes. You might prefer features of Python, Ruby, Angular or Clojure, but you can't write an app in Python and expect it to appear as a native app on an iOS device. Apple, in its infinite wisdom, has decided that Swift is the successor to Objective C and that apart from that language, it is the only one you can use to create apps for its devices. On the back end, of course, you can serve up data and content using anything you like (go cross platform developers!).
The popularity of Swift has skyrocketed since its introduction, but I think if Chris Lattner, the Apple engineer who created Swift, had worked for PowerBuilder, Swift would not be such a big deal today. Developing for iOS is where the money is, both now and in the future, so that's probably the biggest reason why Swift is so popular.
However, there are other reasons! The beautiful irony is that while Swift is the only modern language you are allowed to use to create apps for the iPhone, Swift has been influenced by practically every other language that exists. Swift takes all the best ideas, adds to them, and lets you take them even further. Why Apple has chosen to trust us with such power is beyond me, but we and anyone else who have to look at our code will suffer for the bad choices we make.