It seems that you either: a) haven't used a Sonos system, and/or b) have a lot of free time and don't mind resetting/rebooting your equipment when glitches happen, and/or c) don't care about multi-room synchronized playback. I won't even mention the audio quality, which on an Raspberry Pi for example, is horrible.

Sonos Just Works — some people (like me) care about that deeply. I have better things to do with my life than fiddle with audio systems. If your hobby is building these kinds of systems, then of course it makes perfect sense to roll your own. But if it isn't, I wouldn't waste my time.