Flat silhouetted icons have a more versatile set of contexts - much like flat text does. Sure, you can express a lot in an icon that's 3D and whatnot but it needs its own stage to 'act' and really come alive, or else it'll just look a bit small, hard to read or a set of them will look too dense and over-egged on a shelf. Maximalism is visually demanding, and whilst it'll look cool, the context is too small for those kind of gaudy claims of some huge game-changer in aesthetics.- It's not I don't welcome them, as I do like diversity, but this is not gonna be some game-changer like when skeuomorphics was binned by Apple.
Most people issues with flat design are the mixing of context. Buttons and icons are not the same. Just like normal text and links are not. And a button that have state (bold button in word processing) shouldn’t behave like something that doesn’t have one (flip button in image editing). Whether you like minimalism or not, these are constraints that impact usability. A lot of current designers eschew them.