Creating an entirely new account for ONE single game and having to swap back and forth constantly isn't a very appealing prospect. I'm happy to buy the game, but not to create a whole new account for it.
It's not really a good one for me personally when Steam is my primary method of communication for some of my friends and family. Switching accounts any time I want to play one singular game, and thus losing the ability to communicate with said friends and family for the duration, just isn't practical.