and between the end of Apollo and the emergence of "new space" companies like SpaceX, we saw them get taken for a ride by those very subcontractors with absurdly overpriced cost-plus projects that were always over budget, late and did the bare minimum to meet requirements.
Funnily, even with NASA's example, we have several instances of Boeing screwing up everything in favor of short term gains. ULA had to be 'forced' into existence by the government, because Boeing was caught conducting espionage on Lockheed Martin and was at risk of getting barred from government rocket launches (which would've left the US with only one launch service provider). They also tried to amend their bid on the Artemis lander competition, potentially after having info on others' bids leaked to them by a NASA insider. They forced ULA to severely limit the capabilities of Vulcan to not make SLS unnecessary (even tried to get people fired for it). Then, of course, we have the ongoing engineering disasters of SLS and Starliner.
I'm also not really sure how NASA fits considering that they have no monetary profit motive. They subcontract everything because that's just how the government does most of its procurement.