Because often someone else is paying for it (organization/investor/government) or the money cannot be used for something else. Another common reason is as a way

Because often someone else is paying for it (organization/investor/government) or the money cannot be used for something else. Another common reason is as a way to circumvent internal politics. In my experience, whenever someone actually had to "foot the bill" for the AWS premium, your argument that the cloud is cheaper overall came under a very heavy scrutiny, including justifying those extra "9s" that increase administration effort.