SmartThings published their API last year, so now it is up to the device manufacturer, in this case GE Lighting, to create and maintain the integration. So you should get in touch with them and tell them your customers want to see a SmartThings integration.
That said, the reason zwave and zigbee are easier is that these have published third party standards for home automation. So far, WiFi and Bluetooth do not, so every manufacturer makes up their own commands. This makes integration more complex. 
The good news is that a new standard, Matter, has been announced and will probably start being deployed late next year. Amazon, Google, Apple, and SmartThings, among others, are all working on it. And many existing devices will be able to be updated to use it.
I haven’t heard anything about Cync by GE specifically: again you could ask them. But in a year or so, we should hopefully start to see much more interoperability in home automation.
To read more about this in a SmartThings context, see the following thread:
Matter - smart home connectivity standard (formerly Project CHIP)
And it looks like they are considering Matter compatibility for Cync, but haven’t decided yet.