How can people forget, when that cost is right there in the price tag? If anything, it's easier to overlook the costs of running your own hardware, since they aren't immediately apparent.

My experience is that people don't understand cloud pricing at all.

First of all they tend to not look at monthly prices, and are seduced into thinking their instances are cheap. Secondly they are seduced itnto thinking they are spending less ops time, though in my experience it's the reverse. Thirdly, people "forget" about extras like bandwidth costs (which are extortionate at all the big cloud providers), extra storage volumes etc.

Then when people get the bill, it often gets back-rationalised as being ok because it's cloud so it must be cheap.

The greatest innovation AWS did was finding a way to get people to pay absolutely insane rates for hosting.

They simply underestimate the ops cost, and often focus on the monthly cost. The thing that cloud providers like AWS are good at, and IMO, the only reason you should choose them, is when you have highly variable loads. Dynamic scaling is something only they can do because they have such a massive scale. Even if you're relative small and cannot justify hiring a sysadmin, there are plenty of consults out there you can hire.