Right, but was the attention on the BNFs? LotR initially rivaled HP for wank, but HP is an odd fandom because you had simultaneous book and film releases. The erratic scheduling for the first four movies combined with "new director" and the fact that the books weren't done meant canon wasn't settled. In that kind of environment, it's much easier to rise as a BNF -- con-organization, fandom organization (Fiction Alley was pretty popular for discussion at one time), writing and/or drawing fanwork, fanwork recommendation... and that was pretty much the state of things at HP's height, as the movies brought in new fans and until HBP, the universe was a wide-open sandbox. (Fuck the Horcrux plot.)

On the other hand, LotR is a closed canon (well, Tolkein is dead -- there's not going to be anything new written, but that doesn't stop the wank) and Peter Jackson announced the movie schedule in advance, the actors didn't change between films, and his style was consistent. So LotR fans arguably knew what they were in for with each movie (up to a point) and had less to wank about, whereas HP fandom had Hermione's Pink Hoodie of New Plot Powers. Star Wars is almost the opposite, in that it has all kinds of "canon," but the sign of a true Star Wars fan is that you hate Star Wars and can fight with another fan for six hours over whether or not X is valid canon.

All three fandoms are huge and can support a huge number of fans (not to mention wank), but Potter fandom (in the era described) was the most conducive to BNFdom and making a movie premiere a chance to see OMG BNF in the flesh.