I saw this phenomenon myself years ago in a completely different domain: machine learning. There are indeed many cases where people will rave about your demos, tell you what you made is awesome, but... they will not come. They'll give you great feedback and stroke your ego and tell you how amazing it is... but they still will not come.

It's really a mind screw.

I wish I had some pithy answer or magic formula, but alas I'm not sure that such a thing exists. You'll find many people who will say otherwise and will try to convince you that this or that methodology or marketing principle is the sure fire One True Way. I don't buy it-- I've seen every approach to figuring out business fail in some cases. If there were some 100% effective formula for doing market research or finding product/market fit ahead of actually making the product, you'd have a significantly higher success rate for new startups. Actually, I bet if such a thing existed you wouldn't need startups. Companies and venture investors could just run that formula and cook up endless successful new ventures without all the gambling on the crazies called "founders" and their unproven plans. In reality most ventures cooked up by "professionals" under such circumstances fail quite spectacularly.

Good luck with all the things you do next!