Some reasons to be discouraged making a solar farm in a desert:
Middle of nowhere, you need to transport all the hardware to the place
Maintanace, you need people on-site to support it
Desert sand is sandbladting your panels
(and this is the biggest one I think). You need to transport the power from where its generated to where is requested. Which is an imperfect proces, and every time you double the distance you also double the resistance
Some reasons to be discouraged making a solar farm in a desert:
Also deserts are not even nearly lifeless. A solar farm of the size needed would wipe out a lot of habitat.
Won’t somebody think of the Fremen?!
This is also why there is a lot of work being done on room-temperature (-ish at least) supervonductors.