I would argue you get what you pay for in terms of interoperability and reliability, but I can imagine people willing to trade some of that for a lower price.
Interoperability comes from standardization, which Zigbee sorely lacked. But actors like Tuya or Leroy Merlin built their own standard over Zigbee, which means anything that has “works with Tuya” will work with any Tuya coordinator of any brand (same for Leroy Merlin ecosystem). And even those who don’t usually mostly works.
With that you’d get ZWave reliability, most, if not all, of its security features, with Zigbee lower price. And they still works great with third party coordinator.
But it is true that Z-Wave uses lower frequency than Zigbee (868MHz vs 2.3GHz). It means lower frequency interferences, and better reliability over high distances.
Another issue is that zwave isn’t available in all countries (or it is but uses incompatible frequencies) so it’s less useful outside the big markets.
