Why was it still difficult to travel from al-ain across the desert

Due to very high temperature.

Explanation:

Due to very hot climate, it is very difficult to travel from al-ain across the desert. Due to the vast desert of al-ain, the people usually travels on the camels and the climate is very hot which make difficult the journey across the desert. The high temperature of the region is due to the more distance from the coastal regions of Abu Dhabi.

answer; eliminate parking problems in cities, because a car took up only half as much space as a horse and buggy;

idk if you found them already or not but you probably did but the one closer to sea level is raleigh.