@codemonkeymike
1- Installing it is difficult and scary
2- You can't just "install Linux" - there are choices to be made (distro, SE) that you don't even know how to make
3- It's harder to find the software you're used to, and know how to install it
1- and 2- can be mitigated by using LiveCD to try things, installing it on that old computer that we all have lying around, and just going with default Ubuntu. 3- takes a lot of getting used to.