Both major manufacturers (A and B) seem to brag about cutting costs by using suppliers. Then, after they cut the suppliers to the bone and the suppliers are unable to produce in adequate numbers with requisite quality, they throw those same suppliers under the bus.
This is true, but the problem has shared responsibility.
The primary manufacturer needs to recognize their dependence on the viability of the vendors, but the vendors also need to be realistic about what they promise. That's something the vendor is the expert on, not their customer. I've seen numerous instances of a 1st tier manufacturer demanding as much as they think they can get (be it rate, schedule, performance, or price), a vendor agreeing to it, and then failing to deliver what they promised.
I've also seen vendors refuse, lose a bid as a result, the winner fail to deliver, and the losing vendor win the next round because their competitor ruined their own reputation by promising what they couldn't deliver.
And I've also seen vendors refuse terms, the customer re-evaluate their requirements in response, realize they are unrealistic, and issue new requirements, taking an especially critical look at vendors who promise things their competition says can't be done.
I've also been privy to contract negotiations where these risks are discussed during the bid process and good faith efforts made to decide which party is responsible for managing which risks. Very often the customer accepts risks in order to get the vendor to attempt to fulfill requirements they believe can be met, but will not guarantee, because it is beyond the scope of anything the vendors competing for the work has done before. Tiered requirements with associated incentive payments are one way of handling these cases.