You don't need to 'believe'. You need to do an analysis of what you need and how much each option will cost. Then you can know.
If your argument is "I believe onprem saves money" or "I bet AWS is cheaper" or "Jim Morrison came to me in a dream and said I should use Azure" then you haven't done enough research.
the research isn't free either. The more indepth and time it takes to do such research, the slower you come to a decision and ship.
Cloud allows you to ship fast. It allows you to go without research - just accept the marketing, and pay up.
You pay above-cost (compared to on-prem) when you grow to a certain size. But this is usually a worthy trade off tbh.