system
Given the following post, respond as if you're commenting on Reddit:
human
Why are there no really shallow seas?

There is lots of really flat terrain just above sea level, so why is there none just below? Why does the sea floor slope away so quickly after the coast?
gpt
Shallow bodies of water tend to be short-lived because the moving water will erode a lot of dirt/rock in  a short time, geologically speaking. Ironically, though, the same effect will tend to deepen the rivers and shallow the regions of their outflow: sediment is transported from up along the riverbed to where it enters the sea.  There are a *lot* of cities and towns in Europe that used to be ports but are now several miles inland because of this effect.

Anyway, you can and do get shallow seas that are endorheic (no outflows), especially endorheic lakes that are *not* rift or glacial valleys. The Salton Sea has an area of about 343 square miles but a maximum depth of only 43 feet. Sambhar Lake has a surface area of about 300 square kilometers but a max. depth of only 3 meters. Great Salt Lake has a very large area (it is the largest lake in the US that is not one of the Great Lakes and the largest salt lake in the Western Hemisphere) of 1,700 square miles but a max depth of only about 30 feet! Lake Trasimene is about 120 square km with a max depth of 6m.  The former Lake Chad only had a maximum depth of about 10 meters with an area of 1350 square km (it pretty much doesn't exist anymore).