Yes I am afraid to say you have very small balls this is the reason they don't hang. Big balls hang low because of their size and weight and men with big balls have bigger ball sacks. Does anyone complain about your small ball size?
This ain't anatomical accurate.
Testicles hang down when there to hot, and lift up when temperature is to low.
The ideal temperature is about 35°c for the production of semen.
So it's all about production and the creation of the ideal temperature.
All up and down going is due muscle action, and doesn't have to do anything with size.
Although aging men do experience the effect of gravity and the skin becoming less elastic.