Simple, you lose energy and get disoriented when changing direction. When flying in a circle, you’re constantly changing direction and at an angle to the ground. So you are consistently being disoriented as well. So you’re constantly on the throttle or have to rethrottle up to gain altitude doesn’t make for constant holding pattern.
Why do you lose altitude or airflow with a circle?
Simple, you lose energy and get disoriented when changing direction. When flying in a circle, you’re constantly changing direction and at an angle to the ground. So you are consistently being disoriented as well. So you’re constantly on the throttle or have to rethrottle up to gain altitude doesn’t make for constant holding pattern.