I’ve written this before and I’ll write it again:
The number of users of Linux is irrelevant. What matters is the number of these users who would be ready and willing to pay for a SketchUp Pro license. Until someone can make a convincing case that there are enough such, Trimble (a for-profit company) has no motive to develop a Linux port.
One must bear in mind that the Linux community is primarily based on free and open-source software. SketchUp has never been open-source, and the main reason there is a free version (Make) is that Google thought they could get Google Earth populated with 3D buildings by giving away a simple version of SketchUp. They abandoned that idea in favor of other methods, and no longer even accept SketchUp models for inclusion in GE. Shortly later they sold SketchUp to Trimble. But unlike Google, Trimble does not have an ulterior motive of selling ads or tracking users by which to recoup costs. They need to see a real market.