What is the name for the economic fallacy or paradox where I see an article like this and thing "$15k over 4 years is not worth my time" but if you were to ask me if I wanted $15k or a small fraction of that right now with no recurring aspect I'd take it in a heartbeat? That's how I feel reading any of these side project pieces. I look at the total revenue and how long it took them to get there and I groan thinking how I'd hate to do that. Maybe I'm just too focused on hourly rate?
That's called rationality. The paradox is thinking it's worthwhile to squander the few free hours you have to make a number go up.
OP made $15K selling snake oil of a specific nature that, if it were a legitimate product, would have made far more than $15K if he simply used his tool himself instead of productizing it and selling it to rubes and crooks.