Question

Why deserts mostly form in the western regions of the continents

Answer 1

deserts are often found in the western margins of continents. It is so because:

The Trade winds are offshore in the Sub tropical high pressure regions  in the western margins. e.g., The North east trade winds blow from land towards sea from the Sahara desert.This takes away the moisture from land towards sea and decreases the probability of rain.

The western margins of the continents are marked by Cold Oceanic currents. e.g., the Western Sahara's oceanic border(Eastern Atlantic) is marked by Cold Canary current. This cold current reduces the evaporation rate of the waters there i.e., no evaporation, no rain.

Thus, both the factors lead to formation of deserts in such locations.