Thats because its not true gsync in laptops its actually adaptive sync. The way laptop monitors are designed allows this to be used it doesnt need a module because the hardware required is already there. I believe adaptive sync is the way forward and would be a "standard" to adopt but the tech for desktop monitors is not available yet. Through the type of DP/HDMI classification or monitor hardware something like that.
Yep, and it was form making adaptive sync compatible mobile GPUS that Nvidia decided it would be a good product for desktop solutions and so went on to develop GSYNC.