Indie games are interesting because you'd think given the nature of their development they'd do more interesting things, but stunningly they've mostly stayed within a few codified genres (roguelike/ deckbuilder/platformer galore). There aren't many successors to the giants of the old like Terrarria or Dwarf Fortress.
I'd have to chalk it up to a lack of vision (I don't genuinely believe someone grows up wanting to make a roguelike deckbuilder), but then that begs the question of why are they in game dev in the first place.
Indie means low budget (although even that is getting perverted), not hobby like development done as a labour of love.
The latter are few and far between, but they have always been.
Can a game historian count the Doom clones that showed up after Doom? Does anyone remember any of them with the exception of Hexen and Rise of the Triad?
You don't think it's because the audience is already familiar with those types of games? It's like asking why studios are all producing super hero movies instead of avant guard indie films.
I'd have to chalk it up to a lack of vision (I don't genuinely believe someone grows up wanting to make a roguelike deckbuilder), but then that begs the question of why are they in game dev in the first place.