The bottom line is Windows is ubiquitous and remains as such because it's "good enough".
The lack of interest arises when people are forced into learning a new OS, only to discover that they are performing the same everyday computing tasks as they were with Windows. In the best case scenario, people may seamlessly switch to Linux and use most of their Windows applications with the help of Wine, Mono, Seamless Terminal Services, and/or Virtualization. For others folks, switching might present a hassle, especially if the problems pertains to hardware.
The result: The switch to Linux encompasses access to the same Windows or native FOSS applications, which more likely than not have Windows ports. For typical users who care not of FOSS principles and ideology, theres just too little advantage to justify a migration.
The cost advantage doesn't really come into play when 95% of the computers sold at retail outlets come pre-installed with Windows; there is really no choice but to pay for Windows in the first place.
As the old expression goes...you cannot fight fire with fire. People aren't impressed by merely being "almost" as capable to the leader. Linux and FOSS need to depart from the endless game of matching/rivaling Windows solutions to surpassing them with software innovation.