Comment by MilStdJunkie

So everyone else here brings up great points, but something else to consider is that the barriers to market entry are, to some extent, created by the OEMs themselves, by dominating the ISO and AS9100 committees and TWGs/TSGs[1]. This means a couple things.

First, Boeing never needs to take an external audit - they wrote the thing - but their suppliers need to cross every T and dot every I or else they owe Boeing money. In the worst case, a supplier can end up handing over product and STILL owing money. But Boeing - and especially BCA - they have never, and will never, undergo an actual AS9100 audit.

Second, since the standards are existing Boeing process, that represents a pretty much undefined cost for any market entrant. And that cost can be cranked arbitrarily if/when Boeing feels threatened, by amending the specs themselves - as they tried to do to SpaceX in 2010. That's probably a story for later, but it's pretty disgusting, although not as disgusting as what happened to the C-Series. OK, none of those are as disgusting as a million other things, but you get the point.

[1] And, to some extent, the FAA itself, but that's a whole other subject.