This is not necessarily true. Wrong monetization can be the killing blow. Market can change and your business model which used to work can suddenly fall apart. A recent example for business model change is Tailwind where traffic to their open-source docs plummeted and suddenly not enough people are upgrading to their commercial licenses.

Startups die for a variety of reasons, even if products are popular and loved.

True enough, though I think Tailwind suffered something of a black swan event of having lifetime pricing plus AI coding assistants hitting an inflection point that immediately and thoroughly decimated the value prop of their core monetized product.

Tailwind was (is?) also selling "lifetime" licenses, which means eventually their sales would collapse anyway, once they have sold a license to most interested customers. They were always going to need to pivot at some point. regardless of traffic to their docs.