What makes DotF so popular?

Im trying to figure out what the "unique selling points" of the series are but Im struggling a bit.

On one hand, it's not that difficult: a mix of cultivation (eastern style) with litRPG (western), a never ending world/universe, endless leveling, endless potential for questlines, Zac is a normal dude, etc etc.

On the other hand: none of this is (or should be) hard to replicate for other webseries, yet very veeery few reach the incredible success of this series.

Is it something about the way the author writes? Is it inventive quests, some other "secret sauce" that is hard to replicate?

I like the series a lot, but I cant for the life of me understand what "IT" factor DotF has that the vast majority of RR stories lack.