Because it makes really tiny images, and most stuff does work even if it's not officially supported.

And if you need to use something non-musl compatible, you just make a container with a different base OS.

My last job we actually switched away from it because of bugs and went back to Ubuntu for container base images

Adding to what josephcsible said, not just tiny but also super simple. I use Alpine on all my routers/firewalls/VM's/physical servers for personal use. I've been very happy with it thus far. Simple upgrades. Easy to debug. All the packages I use appear to be compiled with decent hardening options. The LTS kernel is just a few days behind kernel.org.

I've not tried to use it as a desktop. I alternate between Void and QubesOS for desktops.