If someone joined because they saw his money-grab video, then they signed up to help him out of a financial crunch, not because they felt his content was worth the money. As others have said, you can only go to that well so many times before it dries up completely.
Patreon does show creators how many people signed up and left in any given time period (with the standard options of 30 days, 6 months, 1 year, and all-time). But I doubt they make those numbers public (and overall, it's much better that they do not).