I can totally see it from your perspective, because the story of the album is not really that explicit in the music itself. It's a very abstract and artistic thing, and it does show that Billie Joe was a rookie on the field of storytelling through song. I think you need some sort of initial explanation fed to you in order to figure out the basic outline of the story, and even then it's impossible to get a detailed idea of the story of the Jesus of Suburbia just through the lyrics, you can only take wild guesses. I'd go as far as to say that if the album wasn't labeled as a "rock opera" most people wouldn't even know there was a fictional story going on. JOS the song could be autobiographical and a reference to it like "the Jesus of Suburbia is a lie" in Are We The Waiting could be just the same. I think a lot of us believe we truly get the story through the music, but I think we give ourselves too much credit, 'cause if it wasn't for interviews, the album booklet and the musical, I don't think we would've gotten it. I remember having asked myself before if it would've made a better album if the story was very explicit and detailed and told in a much more straight forward manner, and I don't think it would've, cause those kind of songs would be very difficult and uninspired to execute. I think songs explain a feeling or a moment in time, not a linear story that goes from one point to another, it just wouldn't work. Communicating a story through song without any dialogue or visuals like in a musical, has to be very hard if it still has to have that feeling of a traditional song. I think American Idiot deserves the "masterpiece" label it's been given - the songs are great, and the intended story is also quite original and interesting, but as I said before it's clear that Billie was new to this, cause some of the songs seem forced into the storyline, and some of the more explicit references seem really unspecific. So American Idiot is a masterpiece because of its music and lyrics, not because it's good at telling a story through it.
But there are some pretty good interpretations out there which are exciting to read, even if it's just a fan's take on the basic storyline.