Why are deserts famous for fossils? Is it a coincidence? Some examples:
Bones don't last very long in jungles. Or in forests. Or almost anywhere.
Fossils are the consequence of one highly unlikely fluke after another. Darwin himself commented on this. It takes just-right circumstances to have the bones of a recently deceased animal not be eaten by scavengers or turned into rot by bacteria. It takes yet another set of just-right circumstances for those bones to turn into fossils. It takes yet another set of just-right circumstances for those fossils to be brought back to surface level. It takes yet one more set of just-right circumstances for those nearly exposed fossils to survive the ravages of time and weathering.
The last coincidence is where deserts come into play. Water is an extremely powerful weathering agent. The key characteristic of deserts is an extreme lack of water. Fossils are much more likely to survive the savages of time without that weathering by water.
Because you find fossils by looking at exposed bedrock, deserts by their nature often have huge expanses of exposed bedrock. The lack of plants is also a big benefit, plant roots tend to destroy fossils
Fossils are everywhere you have sedimentary rock* deserts are actually rather poor at forming fossils compared to many other environments. They are FOUND more often in deserts because there are no plants or soil covering them up and no plant roots to rip them apart for minerals. You do not need deserts just exposed bedrock. Keep in mind what are deserts now, were rarely deserts when the fossils were buried, your own examples of localities were estuaries, floodplains, and shallow seas respectively and are places far more likely to form fossils.
Fossils in other climates are commonly found during road cuts, mining, or large building projects, situations where all the soil is removed exposing bedrock, which of course makes searching the bedrock possible. In many deserts the bedrock is already exposed meaning all you have to do is wander around until you find a fossil poking out. It is far easier to just wander around a patch of desert and search with your eyes then dig up random portions of a forest hoping to find fossils. searching for fossils is almost always visual, which means you need to be able to see the ground and not plants covering the ground. Although in deserts you can use plants, if you see a wide expanse of open desert soil and a single plant, unless there is a water source that plants roots are often wrapped around a fossil, the added minerals from the fossil helping the plant grow better than those around it, plant roots are very destructive and tend to seek out fossils.
The best environments for forming fossils are often wet, floodplains, estuaries, and lakes are great for forming fossils because they have a lot of deposition and the first step in fossilization is burial. Deserts which often have little sedimentation are pretty bad at forming fossils, but they make searching for them so much easier. Quite frankly there are not many paleontologists and they are human, so they tend to hit areas with high chances of finding things.
there is one other factor, people often don't like paleontologists digging up their property or slowing down construction, but people or governments that own stretches of desert often don't care if you dig up portions of it. So in the desert lucky finds will get expanded exposing more and more of the right layer, while in other environments this would not be economically or legally feasible.
examples of famous non-deserts, Solnhofen Germany a giant limestone mine, La Brea tar pits, heck the first complete fossils skeleton ever found was found in New Jersey in a coal mine.
**Not every sedimentary layer has fossils, there is a geochemical and physical factor, but a surprisingly large number do.*
I would contend that the fact that the location is a desert has little to nothing to do in most cases to the existence of fossils at the location. Most of the fossils in the location, at least the ones that make most headlines like major dinosaur deposits, were left there millions of years ago. The fact that a location today is a desert has no indication of what the climate, or even where on the globe that location was 50 or 100 million years ago.
Do not forget about plate tectonics and climate change. One can go to places like the Judith Basin in Montana, a relatively harsh area of North American Bad Lands, desert or near desert like conditions with cold winters and find fields of fossils from animals that are believed to have lived in tropic marshes of in oceans, because at the time those animals lived, what is now Montana was not inland, and was not at a Northern location. Millions of years ago it was an undersea plate, thus it has layers of limestone made from ancient single cell sea creatures and sometimes larger objects that were entrapped and preserved as larger fossils. At other times, those plates rose from the sea floor and homed some of the large creatures, like T-Rex that lived, thrived and sometimes survive as fossils.
Later, that plate move and ended up inland, in what is not North America. Glaciers, wind, and water may have stripped off many layers of deposits and left exposed or close to exposed the layers of interest to fossil hunters. Desert regions tend to be subjected to this type of erosion and exposure making such finds easier. If those same fossils were in and area such as a rich planes area with plentiful plant growth and never subjected to glacial scouring, they could be, and may very well be, right below your feet but under many layers of soil and decaying vegetation, river sediment and other deposits rendering them out of sight and out of reach.
Because there is nothing in the way. Looking for stuff in a jungle is difficult because of limitation of vision and difficulty of moving equipment and supplies. Looking for fossils in downtown Duckburg is difficult because local ordnance prohibits digging big holes. Deserts, while hostile, are easier to traverse and cater.
Many fossils in the UK are found at the beach where the sea and weather erode the land to expose the treasure, and in mines where people are free to dig to their hearts content.