The way I look at it there can only be two reasons:
- It's just really good and so is spreading virally.
- Everyone is being asked to install it by some educational or training body - maybe it's on some curriculum somewhere.
Having Goggled around and wasted more time than I really should have I came up with nothing except that Edubuntu comes with it installed (and surely schools are using that?)
Anyway, if you have any ideas then let me know. Meanwhile I'm just sitting here playingr gbrainy like the rest of them.
There's a neat article here.