Left 4 Dead 2 - purchase non low violence version? [duplicate]
It's probably because of the country you are buying from. I believe someone can gift you the regular version if they buy it in a country that allows it.
Alternatively, you can buy the low violence version and use the instructions found here to enable the gore:
http://www.destructoid.com/blogs/Skribble/left4dead2-australian-gore-fix--153748.phtml