Automotive suppliers pretty much care about 50 cent parts holding up OEMs, penalties are prohibitively high for a reason. An in-house fab is, as you said, probably more expensive. Simply because it has to rely on a single customer. Show me one company that is not looking at costs, one way or the other, that stays in business in the long run. Not doing so has, yes, something to do with savings on the procurement side (errors were made there as much as everywhere else). It also has something to do with long-term survival, and that does include jobs (even if that turned into a trope by now, there is some truth to it). Not every company can use VC money to bolster competitiveness, most have to compete on cost, and there every cent counts. Especially when we talk about high-volume products.
Which works, until your supplier is simply willing to go bankrupt. And you still have no chips and can't ship anything.
> most have to compete on cost, and there every cent counts.
Until you can't ship and everything grinds to a halt. Risk reduction has a cost and nobody is willing to pay it because it doesn't enter the balance sheet.
