Build small, re-iterate big?

Recently while working on a product that we are yet to launch, I experienced an interesting user test scenario, something which I have not been able to experience with startups, especially in the Indian ecosystem. We had initially built out a basic prototype to entertain a use case that we have now iterated on, this prototype though needed to be scrapped almost entirely - gave us access to 1. A list of active users trying to solve a similar problem 2. Relatively high amounts of data about each user both static and based on the problem-solution scenario 3. A system that enabled us to break down our product thinking into atomic parts and focus on the key pain points 4. Clear understanding and picture of the actual problem scenario, or at least that's what we think and are building out our next demo to test out. Of course this was not the first time the lean methodology of designing a product worked out, but this was in my recent past and one of the more unorthodox runs I have had. Why is it still that we only see a handful of startups take up the build out an MVP - test closely - reiterate - launch based on core problems and not what we think is the solution route?