Gentlemen:

"The two greatest successes of U.S.-Saudi cooperation, coordinated support for the Afghan jihad against Soviet occupation and the Gulf War, (both) created the conditions needed for the September 11, 2001, attacks."

"Saudi Arabia was the top destination for U.S. arms in 2014, and the trade is expected to grow 52 percent in 2015 to $9.8 billion."

Two quotes found here:
U.S.-Saudi Relations - Council on Foreign Relations

IMHO:

Knowing that the Saudi's, have always had their own agendas, one of which is to maintain the status quo ie: royals ruling Saudi Arabia with the able assistance of the the followers of Sheikh Mohammed Ibn Abdul Wahab, conservative Sunni Islam.

Profit alone cannot insure the status quo for the royals - without weapons.
And, weapons (circa 2016) with dwindling importance as drones/robots/space based technology etc come online, still require substantial manpower and expertise. Until now, and perhaps continuing through this decade, the United States has been doing the heavy lifting - all that is required to keep the royals in power, in return for the Saudis investing oil profits in U S concerns, and playing American baseball with pice of oil.

Recent events have shaken the Saudi belief that the United States is an able partner and agreements dating as far back as the 30s, ARAMCO, 1948 etc have been covertly renegotiated and the current price of oil has much more to do with this change than with the profit motive or a potential profit
motive .

xfiltrate