While Darktable and Rawtherapee are free and capable, the big difference is how oriented they are towards productivity. I’d say they’re not at all!
DXO is much better in this aspect with custom palettes and the presets etc, so I’d say there is a tangible difference for pros that need to process a lot of photos in a fixed amount of time - there is no viable linux alternative for that, so at least for me after having tried the Linux alternatives you mention, the productivity with DXO is much higher for similar results.
This together with Adobe increasing prices again and again, drives more people to other alternatives, and many abandon windows too for different reasons, so while I agree with your arguments, maybe it’s not quite as true as it was a few years ago?
Another semi-aproach could be to at least implement and document a not-officially-supported way to run DXO in wine. Linux-users are perhaps usually more computer-crafty so if it’s a simple fix, it may be worth it and result in a few more sales. I have tried and gotten it to install and a bit into the program start (using winetricks for .net 4.72), but no cigar, and I can’t tell if what’s left is a lot of work or just some detail they could easily fix. If wine-support is achieved, I don’t think a docker/snap should be far away so almost “anyone” could install DXO on linux, but I understand there’s still a huge gap from this to officially support it (QA nightmare if using wine etc…) so it would still be unofficial, but could attract some people, and if slowly working in that direction become a major player on linux over time. (DXO seems to be based on .net and Microsoft is working hard on the next major .net-variant, .net core, which runs on linux so it might not be that far-fetched).