None of those technologies worked very well though. WiFi direct and bluetooth have the problem of being too long range. How does the transmitter determine who the receiver is, for example? This is why they made "bump" apps, because it was a useful kludge to solve the hand-shake / setup problem. And IR never worked very well and was far from ubiquitous, and hasn't been present on modern smartphones regardless.

NFC's advantage is that it just plain works. We'll see if it catches on, but it does cover a set of use cases that is fairly meaningful and has yet to be served by a truly robust and seamless technology.