It’s because of gear ratios. For each movement of the first gear , the second only moves a fraction of that, let’s say 1/20th. If the first gear moves at 1 full rotation a second, the next gear moves 1 rotation every 20 seconds, the next 1 every 400 seconds, and so forth. It adds up quite quickly, the tenth gear would take 16,235 years to make a full rotation in my example.

The picture above may or may not need more time than could exist in the universe to see any moment in that last gear.