I've thought about this myself. The thing is, the two libros have absolutely nothing in common, except one major thing: the fans. Think about it: before Twilight, Harry Potter was the most popular teen series. HP gained fans who loved the series and thought it was the best series ever. Along comes Twilight, which gained fans with the same "best series ever" attitude, and all of a sudden, HP fans are saying "NO! Harry Potter is the best book series ever!" and Twilight fans say "Oh please! Twilight is better!" and all of a sudden you've got this "war" between fans who are completely convinced that their book series is "better". Think about it: would tu be on this spot if tu didn't think that which ever side you're on's book is better?
Like Madam_Octa said, the fans are one of the main reasons. But another huge reason that started the comparison and the fights, was what the media started to publicar and say. ' Twilight is the new Harry Potter!' and things like that, I know for myself being a HP fan, really got me annoyed. Just look at the back of the Breaking Dawn cover - "Move over Harry Potter!". I wanted to puñetazo, ponche whoever dicho that in the face. -.-
At least, I THINK that's one of the reasons. Correct me if I'm mistaken. :)
Can say that i wondered this like over a million times , i am a fan of both but honestly i couldn't ever see anything they had in common except that Robert Pattinson played in both movies.First of all Harry Potter is a kick-ass adventure,fantasy book(movie) while Twilight is a romantic fantasía book(movie).So the segundo thing that they would have in common is the fact that they fantasía but heck there are a looot of fantasía book, and in the end all this comparison comes from the press cause they did it the first time and that was just because Rob played in both.I honestly can't see the comparison but eh who the hell cares what i think.