The problem with ball carts

The balls at the bottom require stooping for retrieval. Who wants to stoop? You could get the shallow ball cart, but they don't hold as many.

Has anyone invented a ball cart that has an interior under tension? You put ten balls in, it sags to allow another ten. You take ten balls out, it pushes the first ten toward the top? It's tricky, I know. Volleyballs don't weigh much. But there are smart people out there!

Or maybe a foot pedal mechanism?

It's a gold mine, I tell you. Build a better ball cart and the world will beat a path to your doorstep. (Of course, if you already have a sidewalk, that could be annoying.)