Another factor to consider is that sometimes the very same heresy can be appealing in some situations and not at all in others. Let’s talk the low-Christology heresy, which has popped up in many forms over the years. It was pretty popular when it first appeared as Arianism. And today it exists in even more forms–Unitarianism, Jehovah’s Witnesses, Christadelphianism, etc. But it’s not equally appealing in all its manifestations!
The Unitarians and Jehovah’s Witnesses have some decent numbers but the numbers for the Christadelphians are pretty low and their churches are tiny. So there is more going on than simply the low Christology heresy. Probably evangelism, brain-washing, and many other factors have a lot more to do with it than simply the heresy.
One thing I appreciate about covid-19 is that it pretty much stopped JWs from knocking at my door–yay! You know, it’s always two people who come around-- a senior JW who does all the talking, and a trainee JW. I direct my questions at the trainee and that ends the conversation pretty fast!