Yes you are right to some extent. They aren't "hard" to pay off in my opinion. They just aren't something that is paid off quickly. If you were to build one designed to mine ether currently, then yes it would be hard to pay off.
As my introduction to the topic before givIng any steps said, "you need to ask yourself, is this really for me?" And I also stated.., "you could lose money".
I agree with you to that extent and believe Everyone should do their research and see if the money invested into their machines is worth it to them.