Its true that aws is very expensive for a lot of use cases, as long as you only count the cost of the servers.

However, in most (every?) large organisations, buying a server and putting it in a DC, and looking after it, is hugely time-consuming, lengthy and expensive.

You need to get quotes, approvals, purchase, rack, commission, maintain etc etc. It is usually close to 1 year to get a server.

In some companies, even getting a virtual server takes almost as long!

With AWS, once an account and service is approved, boom, you are done.