Linux will never be the top desktop operating system simply because it is "free" software. People are less motivated to work for "free" and without money. The software produced tends to be released half-finished when only one set of features are complete, relying on others to finish the work. Usually others do not contribute at all, so most projects die or barely remain functional.
Until there is proprietary funding into Linux programs, userspace and kernel, it will never become _the_ desktop operating system.
What evidence do I have for this?
First, look at Android. The only reason why it is so heavily abundant is because of that big proprietary money that Google, the telecoms, and the manufacturers put into it. Do they release all their code back to users? Hell no they don't. Most of it is proprietary. They don't have to release it back.
Then look at Ubuntu. Arguably the most successful Linux distro on the desktop, but that's only because of Canonical's ability to raise funds and invest into their own products. It's different enough from Linux to really be on its own merits at this point.
I could find others, like RedHat, SuSE, etc, but I won't.