Time is not free. It may feel like time is the cheapest currency you have, but the reality is the opposite. As a founder you only have a handful of opportunities in your life to build companies, which means the opportunity cost is higher for a founder than anyone else involved in the startup ecosystem.
Founders often don’t start a company based on ROI (Return On Investment) analysis. They start them because they believe in something. Even without building a financial model they start iterating on a product, often for months at a time, until it gains customer traction. Starting with a blank piece of paper the only guarantee is that a new company will cost the founder money.