That list seems to conflate "popular" with "most circulated". As some people in the comments on that page have pointed out, the two things are not comparable, and also the WT and Awake are distributed without charge, while the others are actually paid for.
There are three possible measures:
- Most widely circulated magazine
- Most widely read magazine
- Most popular magazine
Of those, I would imagine that WT and Awake might top the first list, but it's unlikely they top the other two.
How do you define a "popular" magazine, if not by sales? Because the reader has not had to part with any of their own money to get it, a free newspaper or magazine may be widely distributed, but may just end up in the bin after a cursory glance. In the UK, we have a free newspaper called Metro which is distributed at bus and railway stations. It's common to see copies all over the seats and floors of trains and buses throughout the day, after commuters just pick one up in the morning, skim it on the way to work, then dump it when they reach their destination. Can it be said that it is "popular"? Perhaps. Or perhaps it's just convenient because it's free and widely distributed.