Making Snapmaker products compatible with 3MF is about joining an ecosystem. It does not mean that customers running operational systems that didn’t join the consortium (yet) would be left on the dark.
Actually it could bring even more customers to the table. Think about it, Apple has the resources to join the consortium and to jump at the 3D bandwagon at any time. Apple just need to want to. Alternatively, building a MacOS driver is a well documented task that would not be that different from writing a Windows driver. Moreover, given how much Google likes open standards, it might be possible that Google also join the consortium and bring Android customers to the table as well.
Keeping a 3D software package development is expensive. Take for example Simplify3D. In order to stay in the business, they charge USD 149 per license. Another example, is Ultimaker (the creator of Cura). They can afford not charging for its software because their business model. By the way, Snapmaker3D takes a piggyback on some Cura components (like the slicer). Incorporating parts of Cura into Snapmaker3D was a good strategy that saved Snapmaker a considerable amount of money. Finally, Ultimaker is also member of the 3MF consortium.
The bottom line is, building a driver for a 3D printer for Windows (https://docs.microsoft.com/en-us/windows-hardware/drivers/3dprint/index) would relief Snapmaker resources to focus in other innovations while expanding Snapmaker footprint.