Similarly I have worked for systems that would sell a highly customized system to a company like Airbus or Comcast or Safety-Kleen and there would be a huge amount of work going into determining what exactly gets sold which again, is not comparable to going to some landing page and paying with a credit card.
If you're selling mattresses or something, maybe that's different.
And that's just a metric you can use to really see if people are interested in your product.
For consumer products what you're saying may make sense, but that is not the universe of all products and opportunities.
I know who needs this, I understand their pain, but its really valuable to understand their procurement process as well. If they need to have sales people as part of the process, I need to know that (and cost it in.)
Talking to my target market, and understanding what it takes for them to pay me, is a big part of understanding if I have a real business idea or not.