The theory of moving to the cloud is that you get access to hyperscaler's vast economies of scale and 0 capital costs compared to on-prem. I've never thought of it as being cheaper in terms of capital, but more flexible in terms of scale and cheaper in terms of IT support required from your tech teams. The idea is that Amazon/Google/Microsoft has better devs and sysadmins than most businesses, so it makes sense that they handle that aspect of the business and you pay them to do it.
I'm not surprised that it's not cheaper, I'm more surprised that people thought that there would be magical costs savings popping up.