The first major problem you run into is that you immediately don't have a defined metric to measure the influence/popularity of the music. The Billboard Charts, flawed as they are, do a fairly decent job of charting what's popular in the US, even if they don't always provide good reasons why said songs are popular. But given that the indie scene has never really had coherent, organized charts, determining the trends and ideas that indie rock adopts over time is significantly more difficult to track. It also doesn't help matters that indie rock as a genre is so varied and eclectic (particularly with some of the weirder, underground bands) and (generally) more intelligent that the sphere of influences and trends aren't as defined and static as those in the mainstream. There isn't the same 'producer-driven' archetypes (like the prevalence of the Neptunes in the early-to-mid 2000s) in indie rock, simply because those widespread 'indie producers' weren't nearly as prominent and powerful as those in the pop or hip-hop scenes.
In fact, if we're going to be completely blunt, the lack of success of indie rock seemed to cause the scene to mutate even further, some segments becoming more and more inaccessible. Outside of isolated points, it's taken indie rock eight years to be relevant on the charts again, and in that time, some acts completely gave up on mainstream airplay and became so inaccessible that even Pitchfork had a difficult time puzzling out what the fuck the act was doing.
And even taking all of that in mind, it would be inaccurate to say the indie bands failed, per se. The majority of them kept on making music, mostly within their own purview. If anything, the indie acts didn't disappear, they just dropped out of sight of the pop charts. Now, there are all sorts of theories why this happened, and I have three that I'll share before I begin the review (trust me, these are both relevant).
