If you accept that then it means that we need to investigate and scrutinize the whole supply chain of any product before trusting it and it would also mean that any company switching even the smallest part of their supply chain would require us to reevaluate their product.
When we buy things (either products, services or software) we consider the company selling it to be responsible for the whole and deferring responsibility to a vendor is basically just saying that you were either promising more than you knew could deliver or that you did not do a good job picking vendors.