Want? or need? The Saudis no longer provide such a significant source of oil, which is why they've invested heavily into renewables in the last decade. Even they know that fossil fuels are no longer a significant source of revenue generation for their country and they are taking steps to wean the country from relying on it.
Can't imagine that the U.S. still relies that heavily on those oil investments. The weapons sales is simple greed, like Jeff Sessions undoing any nascent signs of prison reform that were just beginning to happen just so Trump Inc. can benefit from the recent gains of the private prison industry since Trump's inauguration. Trump's own private Halliburton.
Now, if you're talking about strategic partnerships in regards to geopolitics in the Middle East, then I might say, you're cooking with gas there. That's more along the lines of a need.
Trump and his Trump Inc. 'business' in the Middle East, well that's a horse of a different color (although unfortunately it is now related do to his position, at this time).