I wish this weren't so but it's true. Microsoft and Apple also have the numbers game on their side, and humans mainly want to be part of the crowd/with the numbers—not outsiders.
There's also the matter of how Linux is developed, developers tend to develop for purposes other than maximizing its usability for end users, that is there's been no cohesive or strategic effort on the part of Linux developers (the Linux community as a whole) to steal users away from MS and Apple (there's no financial incentive to do so).
It's the 'individuality' of Linux that hinders its widespread adoption.