Deserts are actually very important to the worlds ecosystem. The Amazon rainforest probably wouldnt exist without the Sahara. A lot of the Sahara's sand is made up of dead plankton and these dead plankton are blown across the seas by strong winds and eventually land in the amazon. These plankton give the soil extra nutrients and are one of the main reasons why the south Americans are so lush with life.
One reason for us not being in a simulation is that we have irrational numbers that are seemingly infinite. Like pi. In every simulation that we are able to do, there is a limit to how precise the simulation is. For example, using pi only to 10 digits is more than accurate enough for any simulation we want to run. If we currently live in a simulation, then we could assume that the creators would do the same thing to save on computing power, but we have found many irrational numbers that never end. There is also the argument that the parameters of the simulation would be dynamic and change depending on more and more precise observation, but obviously, that's impossible to know.