If you use a standing desk 20+ hours a week, you aren't sedentary. People who are stuck being sedentary won't be able to move to using a standing desk unless they stop being sedentary. There's a big gap between being sedentary and getting proper exercise.
Sitting allows people to spend a lot of time moving very little, in addition to time spent sleeping. Standing involves a fair amount of effort.
Just because using a standing desk often is a sure way for a person to not be sedentary doesn't mean it's the best idea. In fact the most sedentary people are probably going to have a hard time adapting to using a standing desk full-time.
Sitting allows people to spend a lot of time moving very little, in addition to time spent sleeping. Standing involves a fair amount of effort.
Just because using a standing desk often is a sure way for a person to not be sedentary doesn't mean it's the best idea. In fact the most sedentary people are probably going to have a hard time adapting to using a standing desk full-time.