Google makes iOS releases for most of their apps, including Duo which is a video chat app just like FaceTime (I'm not now, never have been, and never will be an Apple user so can't speak to specific features).
Apple has always had the goal of isolating their customers within their ecosystem as a core business strategy. While selling it as a major convenience (everything just works!), the real goal is to make their customers more and more dependent on Apple's product offerings so they'll never stray elsewhere.
It was a stroke of genius to extend that pressure to their existing customers' social circles with things like iMessage and FaceTime. There are plenty of other options to do exactly what those or any other Apple apps do, with no restrictions on OS. Google makes iOS versions of almost all of their apps. But most Apple users just won't stray.
I'm not arguing that it's not actually convenient, I'm sure it is. But I'm not a simpleton and would much rather have the versatility, customization, and choices offered by Android and multiple manufacturers while having every bit as much functionality available to me as an iPhone, much more honestly. But I definitely don't give a damn what someone else chooses to use.