Here's why:

* 200 kilometers is 124 miles. Continental shelves are underwater extensions of continents, and they are much shallower than that.

* The typical depth of a continental shelf is around 130-150 meters (425-490 feet).

* The outer limit of a continental shelf is usually defined as a depth of 200 meters (656 feet). This is known as the shelf break, where the shelf transitions into the much steeper continental slope.

Therefore, 200 kilometers is way too deep to be the maximum depth of a continental shelf.