So who is Chromecast Audio for?

When I first heard about Chromecast Audio, I thought wow, what an incredible idea, turning "dumb" speakers and sound systems into what I've always loved about my original Chromecast - a new age solution that is dead-simple to use and just works. With news coming out now about multi-room sync, I thought it might be a good time to pick one up. That's when I realized that I wasn't really set up to take advantage of it. I'm a millennial. I live in a small apartment. I have a Big Jambox and a regular Chromecast. Literally zero need for a Chromecast Audio, let alone any compatible hardware to plug it into. So let's fast forward - I have a house and a nice 5:1 entertainment system. I can plug Chromecast Audio into that and play my music, yes, of course, but my original Chromecast already allows that - the only benefit is it would free up the TV to watch sports on mute or something I guess, but if I'm watching the game, I want to hear the game! So back to multi-room syncing. Are there really people sitting out there with... I don't know, standalone speakers with aux ports? If I had a house and wanted to set up 4 speakers to play music simultaneously, I'd probably look at Sonos which has that capability built in (and is unreasonably expensive). What's the alternative? How does someone like me take advantage of Chromecast Audio to set up a modern multi-room music system?

I realize this is probably a really stupid question, but every multi-room system I've seen in the past is either (a) all hooked up together anyway so it plays from one central receiver, or (b) is a Sonos system. What's the cheap and innovative way to accomplish this the Google way? I'm starting to think Google should be selling optional "Google-ized" speakers built for Chromecast Audio or even with Chromecast Audio built in.

I'm rambling - help me understand!