That one was answered a while ago. Because zwave2mqtt relies on the node wrapper for openzwave and then adds the complexity of translating zwave items to MQTT items.
While ozw Dämon just puts zwave stuff on MQTT topics without translating them into MQTT lights, MQTT covers, etc.
Ozw daemon is the slimmer, easier to maintain solution. Personally I prefer the zwave2mqtt approach as I do most stuff in node red directly via MQTT. While this works with ozw daemon as well, zwave2mqtt topics are nicer to work with.
I would love if zwave2mqtt would have been the basis but I understand ozw daemon follows a different design idea which is makes a lot of sense as well.