I haven't called anybody idiots. There are genuine reasons for using AWS specifically. I've been consulting to several companies helping them to manage their infrastructure, and more often than not it turned out that they chose AWS "because everybody is doing it", not because they understood the tradeoffs well.
To be more specific: (1) they were not able to calculate the overall costs upfront. Yes there are many calculators, but you know the actual cost only when you receive the bill. Moreover, there is no hard cap on costs - people have been asking for it since 2006, and AWS was first saying they understand it's important and will take care of it, but in the end decided to ignore it.[0] Yes, you can set up alarms but that's not what people want. (2) AWS is marketed as saving on IT staff costs but it's ridiculous: you need competent staff to support it. The AWS infrastructure is huge, it's a whole ecosystem in itself, and it has its particular quirks. You definitely need smart people to run it and stay out of trouble. (3) Very often when you run a cost analysis of a particular aspect (like storage, processing etc.), it turns out the difference between AWS and, say, bare metal is enormous and, consequently, increases radically with the amount of resources used. There are several large companies who decided to move from AWS to bare metal just for this reason, saving enormous amounts of money.
Now, there are several scenarios where it doesn't matter, or it matters but it makes sense to use AWS anyway, but in my personal experience this is minority of cases I had to deal with. I have nothing against AWS per se - also, there are some aspects of AWS infrastructure that are a pleasure to work with. Nevertheless, usually it makes more sense to use a whole ecosystem, and the more you get locked in, the more difficult is to get out, and the sunk cost fallacy is omnipresent among companies of all sizes.
[0] https://forums.aws.amazon.com/thread.jspa?start=50&threadID=...