Ultimately, the reason that the startup died was because I did not do the due diligence in discerning whether this was a problem that I genuinely wanted to solve with my entire being. That's the bar for creating a successful startup, you need to find a problem that you're willing to dedicate yourself entirely to solving.
My own startup journey has led me to a contrary belief: At the earliest stages of building a business, being flexible and continuously re-evaluating your assumptions in order to find real market opportunities is more useful than having a lot of passion solving a single problem.
If anything, I've met many many founders who have had too much passion about a single problem, which hurts them gravely when they refuse to consider the possibility that the problem they are passionate about is not a problem at all and they need to pivot.