Geopolitics of the 50's, 60's and 70's were bi-polar between USA and USSR.
What was good to keep the Russians from expanding its brutal regimes was having strong Dictators who sided with the USA.
In the middle east we also needed to ensure oil supply. With our support of Isreal it was necessary to have Kings and dictators in our back pocket. The second objective was to keep the USSR from the middle east.
As the russian threat changed in the 90's these old dictators needed to become more democratic. The USA policy had shifted from supporting regimes to supporting democracy.