my point is - why specifically is HANON the most popular exercise method?
I've already answered to this one

HANON is specifically the most popular exercise method book because HANON is the only book that made a lot of promises that can't be kept
Hanon promise people that:
1) just with one book you'll get all the technique needed to play pianos a virtuoso a the whole book can be completed in less than one year
All other method, either don't make such unrealistic promises or deal only with one specific aspect of technique, not the whole technique matter
So, when a student want to become a good pianist quickly it is eager to try a method that promise you to provide you all the technique you will ever need in less than a year
No other book has such premises and that's why HANON is more popular than other technique exercises books
Daniel