I agree with you in principle, but they're not going to reform because reform is in they eye of the beholder. For them everything is fine. They don't care how many gray hairs it costs you.
Given that, it seems to me wise to look for ways to make purchasing less nightmarish without needing to reform several thousand large bureaucracies.
Even in the "happy path" where vendors accept POs, 30-day credit terms etc, the purchasing process is still a nightmare, even if it's less so than for card payments. And it's not "just" about stressing out those that interact with the purchasing process - big organisations waste a lot of otherwise productive hours, affecting their bottom line.
When I consider the vast sums of money wasted by the purchasing bureaucracy where I work, it boggles the mind.
Everyone knows it, but inertia and fear of change are rampant in large organisations.
Given that, it seems to me wise to look for ways to make purchasing less nightmarish without needing to reform several thousand large bureaucracies.