Why were all the tombs and mortuary temples in the Middle Kingdom of Egypt ( 2040 to 1782 BC) on the Western side of the Nile?

There are two reasons that tombs and mortuary temples were built on the west bank of the Nile. The first is that west was seen as the place of death, for the sun-god Ra set in the west each day, and the pharaoh's soul would join with the sun as it descended. Cities and and villages were on the east side of the river, associated with birth and life (the direction from which the sun rose). Second, the earth and bedrock on the the west side was better able to support the large structures, without sinking into sand.


https://www.earthtrekkers.com/west-bank-of-luxor-best-things-to-do/
https://www.laits.utexas.edu/cairo/history/ancient/ancient.html
https://www.sciencedaily.com/releases/2008/03/080328104302.htm