AWS is great if you have lots of money and little time. Which was very true in the last ~decade, where we had lots of venture funded startups that had very much money, but little time.

Also, while you definitely pay a markup, the standard EC2 pricing also contains instant availability. If you skip on buying a car and instead pay a taxi to wait 24/7, your costs will also be insanely high. Additionally, AWS provides a great ecosystem where your app can easily be managed in - things like getting a https certificate, setting up a redundant load balancer and even a CDN, database or a Kubernetes cluster can be made simply with a few clicks in an UI. If you don't have someone who knows how to configure those services, it can detract a lot from what you're actually trying to do as a business. Lastly, it has all these enterprise features you suddenly need - solid billing, encryption, certificates etc..

Don't get me wrong, it's expensive, but there's a reason so many businesses use AWS.