But WHY?

Imagine the earth rotating around the Sun, even if gravity is much much stronger than dark energies stretching, it seems over time those micro stretches would still add up.

The earth would be moved a tiny bit from the sun, but is moving too slowly for that orbit, so it moves back down, but now is moving a tiny bit FASTER. Rinse and repeat and it would gain energy and thus move away from the sun over time.

I expect that explanation is wrong, but why? And why do gravitationally bound objects not gain potential energy from their stretching?

This article explains WHAT but not WHY