Why do Middle Eastern employers prioritize candidates with Western degrees?

1 - because Western universities allow students learning through the latest scientific and practical applications2 - the presence of modern scientific material may not be taught in arab universities

because they think western people holding a qualification better than others

Exposure is the key factor there.
Nothing else.

they think that they have more experience

Middle Eastern employers have an impression that Western education is better than anywhere else.
They think that most Westerners are the experts so having a degree in western countries gives an edge.
Westerners are mostly consultants and are in senior management positions whenever they are employed in foreign countries.