I think the reasons go far beyond the lack of flashy ads. Linux is great, I've used it on the desktop personally for 20 years. But there is a lot of technical inertia that would have to be overcome, a huge number of applications that aren't available. I'm not sure Linux will ever become the dominant desktop OS, or if that's even necessary. Linux isn't only a desktop, it's in servers, mobile applications, IoT devices, etc. It exists for people who need it, but depending on your use case other options may be better.