Are bands like radiohead or king crimson not
that mature?
IMHO, the most mature form of music is when it transcends to the level of sublimity, when it goes beyond the borders of entertainment (check out oscar wilde's philosophical argument on art vs. entertainment), when it just becomes art and contributes to the value and realm of the art world itself.
If you want to hear sublime and serious kinds of this artform listen to classical/art/serious music - from bach to stravinsky to john cage.
"art for art's sake"
FWIW