They won't because no one currently can demonstrate how to get devs paid (which is a long complicated chicken or egg problem). I love Linux to death but I'm not optimistic that it will in any pure form compete with Windows as general users are just to enslaved/entrenched with Windows. Of course if Linux replaced Windows as the first OS that people were exposed to then there might be a chance. In the mean time with mobile (pads,phones) taking center stage for most consumers the whole subscription based software as a service model is probably going to take over and tradition desktop OSes are going to decline.
I'm not sure what you mean by developers getting paid. Do you mean to develop desktop applications that work on Linux or developing the actual kernel and desktop environment? If you meant the latter, it already happens. There's the Linux Foundation, Red Hat, Canonical, and other companies/organizations that pay developers to work on their flavor of the Linux desktop and contribute back to the community.
Application developers will be paid the same no matter what platform they are coding on.
What I was saying is that in the mobile space (tablets/smartphones) Linux is king. It outsells anything else in the market by a long shot. One reason being the low-cost of entry (Android is essentially free), the other being that from the outset they had support from the entire lineup (hardware ----> software ----> customers).
We're missing multiple levels of support on the desktop side of things in the Linux community, and if we have more big players in both software and hardware coming to desktop Linux, we're looking at a formula for dominance in all spaces (mobile, desktop, embedded, and server).