I do think a lot of that popularity was because it came out when internet forums were a novelty. If you're used to only one or two people liking the same book as you, then you see thousands liking the same book, that book must be popular.
Then the popularity fed itself. Movies, merch, games, everything was done to capitalise on the "popularity" of a new series, and this introduced it to a new audience. Media started to talk about the new book series that people were going mad for. People who didn't read the books wanted to find out what everyone was talking about. Time passes, and people look back on the books with nostalgia goggles. Even you, when defending the book, can only point to its popularity as an argument.
The actual book doesn't matter. It's popular because it's popular.