It is not just the USA. The UK is a major manufacturer and supplier of military equipment to the Saudis, as is Canada. In fact just about every NATO country sells a significant amount of armaments to the Saudi military. Take a look at the wikipedia page for the saudi army and saudi air force and examine what aircraft, vehicles and weapons systems they use.

There are ongoing operational maintenance and training contracts worth billions. US "advisors" employed by major defense contractors are in Saudi Arabia right now training the Saudi air force.

https://www.google.com/search?client=ubuntu&channel=fs&q=uk+...