Z-Wave v. Zigbee largely stemmed from some awkward licensing to implement Z-Wave.
I think the thing driving Matter-over-Thread seems to be a desire to have more commonality with IP stacks, notably Apple's Homekit not having the adoption Apple wanted and Apple deciding to maybe go with something that the device manufacturers will go for, but not wanting to have to have a totally different stack for dealing with Zigbee vs. wifi devices.
So here's Matter, based on IP, with endorsement of 'Thread' as one of the transports. Now talking to a Matter device over Wifi is pretty similar to talking to a Matter device over Thread, except Thread is not generally IP routing.
So Thread is an inherent mesh design, unlike Bluetooth or Wifi, and low power. Bluetooth kind of sucks for this application since it's peer to peer. Wifi somewhat better but it means you have to inject access points even if coverage could be had mesh-style, with a light switch serving as a perfectly viable relay while doing it's job otherwise. Also you have an actual shot of running a Thread radio on modest battery much longer than Wifi.