A US company will typically have a lot of employees with signatory power, not just CEO+CFO. However not nearly as many people as are issued corp cards. That is often an incredibly low barrier (e.g. at my company I believe literally every employee can get a corp card).
And it's an important legal distinction. If I sign a contract with a company and it's signed by someone with signing power, I can assume that this will have the company's backing (unless I was aware of fraud). I don't have to care if the employee got the right approval for that, the company will have to fulfill their obligations. That cannot be said for any decisions made by anyone in the company.
