Because it's only become marginally hardy (without some protection) here in the last decade or so. Myrica cerifera is only hardy to 7b. Even now, weather like we had in '03 (4 degrees F in Knoxville) could cause some problems. But mostly, it's still a new thing for this area, and many people still aren't familiar with it. There are some commercial growers here in TN that grow this plant now. It's likely to start gaining in popularity.

I lost 3 beautiful ones in Memphis to the cold several years ago. Maybe they are coming out with a variety that is more hardy. I hope so.