What about them? Have you ever peeked into how much market share do they have? Let me guess, no. And Chromecast? Nobody knows what that is aside from geeks obsessed with Google.
Chromecast is currently the 2nd best seller product on Amazon in the Electronics category, having recently dropped from 1st where it stayed for months. On what exactly do you base the idea that nobody knows what it is?
If you compare the reach of AirPlay against the reach of Chromecast there's a difference of at least TWO orders of magnitude; that's my basis. And I'm not an apple fanboy (gohrt), I'm more of a reality fanboy.
AirPlay is not a device, it's a technology implemented by multiple devices, and it's four years old (compared to Chromecast, which is barely one). Comparing the two directly is nonsensical.