Some people are into ultra light credit card touring. I see that all the time.
But if you are asking why not unsupported ultra light touring the answer is probably that most people don't care enough to go through the effort. The fact is to start getting ultra light you have to go through your gear and become very specific as to what you do and don't bring and often need to repurchase items. For most, the payoff isn't there. They can do what they want with what they have. If I can do my tour with my bike and my panniers, why should I reconfigure everything just to go lighter.
It only starts to look attractive when you can't do what you want with what you have or if you really get into ultralight for its own sake. I wouldn't say that's unpopular as much as it is less mainstream.
Last edited by Happy Feet; 11-05-15 at 07:41 PM.