No, it's not simply nostalgia that's driving the popularity of retro style games, it's the fact that corporations had spent years making numerous diverse existing game franchises fit a handful of popular genres. Castlevania became God of War, Syndicate became a corridor shooter.

They tried to make XCom a 3rd person cover shooter, Resident Evil became an action franchise, the first person shooter genre as a whole just became bland military shooters. Whole genres were discarded, with existing franchises railroaded into whatever was popular.

You're not just enjoying indie games due to nostalgia, you're getting to experience a wealth of different styles and genres and gameplay mechanics that had been strangled out of gaming, because corporate wanted every IP to be a billion dollar franchise or nothing.