After all of those decades of oil wealth they somehow never developed the technical competency to build their own missiles. Contrast with Israel which has only about half the GDP, or Turkey which has a similar GDP.
or maybe you would think they are "not allowed" to develop their own arms?
That's one way to look at it. Another is that it's a clever budgeting strategy that outsources all the expensive R&D and production costs to their biggest ally.
Israel took and continues to take billions of dollars of funding from the US to develop its military so a completely baffling example to cite.