Endoheric Basins and Aridity

I’m sure I’m missing something obvious, but is there any reason why larger endoheric basins seem to exist only where it’s pretty arid?

Does the one cause the other (endoheric makes for arid land; arid land makes for endohericness)? Is it just that if there were enough rainfall in an EB that water’d fill it up and carve a way out?

Basically, yes. If there’s plenty of rainfall then the basin will usually fill up until it finds a way out. Alternately, the rainfall itself may carve a way out through erosion around the basin’s boundaries.

Evaporation more often than not has to equal or exceed rainfall. If more rain falls than evaporates, it will fill up until it finds a way out.

For an absolute classic case, see what’s been done to the Aral Sea, which is tiny compared to its size before modern man got ahold of the rivers feeding it, irrigated the water wastefully over the lands, where it evaporated and the sea has almost disappeared.

Thanks to Jordan River irrigation also, the Dead Sea is dropping about a meter a year and may soon disappear completely unless Israel or Jordan follows through on plans to pump seawater in from the Gulf of Aqaba.

Similarly, the Great Salt Lake has those marvellous racing flats nearby that used to be seabed until it seems climate change has managed to tip the balance.

Or consider the Three Gorges (pre-Dam) and what must have been there before the water cut a nice deep groove to escape.

So you find the basins in dry areas because the wet ones escape as soon as they are able. Google Lake Agassiz.