I think the point is that if the Linux kernel "costs" say 4 billion to make, that it's perfectly within the capabilities of a company
if they would see the value in doing so - which has been greatly reduced because Linux works so well for so many people and companies.
But if Walmart needed a kernel for some reason, and it would provide value to them, they could afford it, it's about a quarter's worth of profit. But, again, Linux would likely do anything they needed, and if it was missing something they could add it.