While Linux Distros like Ubuntu make it really easy to set up a developer system (with localhost web, languages and database) it is even easier on OSX via MAMP: install MAMP, configure with a GUI, ready to roll.. Linux you might be tweaking some config files to get the optimal setup.
On Linux you are partially a dev-op not only working on your code but also learning and tweaking your OS, services, etc. for one reason or another.
Another factor is there are some shinier tools on Macs, (i.e. the Adobe lineup, and a easily installed Sublime Editor) And many that went to learning institutions will be comfortable more with Dreamweaver/Photoshop/Illustrator than Eclipse/GIMP/Inkscape.
I took the Linux route, even though I already owned a Mac, I felt on Linux I was closer to the metal where Mac OSX had too many safety rails (both for the user and many publisher's safety)