Which is what businesses should have used instead of putting hundred of millions in a bank. Banks can't magically change economics. Money markets were created exactly for this purpose. This should have been taught to every founder by every VC.
If I understand you correctly, you're basically saying why use a bank versus something else? My answer would be because for vast majority of retail bankers it doesn't matter. Same reason many would use Gmail vs self-host. They want to put their money somewhere and ensure that it will be there when they need it. As a society we have a framework around that and we provide deposit insurance and we call the orgs who take your deposit, give you an IOU (in the form of an account balance) then lend a fraction of it to others a bank.
For significantly larger sums no I don't think it makes sense to use a bank and most large corps have a treasury that specifically deals with that.