Birth of the Cool
One can grant that formalism once served a purpose as a stopgap against the crass instrumentalization of art in the service of adorability. Where formalism failed is where all modern antimodern ideologies fail, in the inability to oppose banality in any but modern terms. Since banality is the product of the desacralization of the world, it cannot be adequately opposed without an affirmation of the sacred. But modernists for the most part preferred a strictly aesthetic opposition lest they come off as reactionaries.
Banality, however, has democratic appeal while aestheticism carries the stigma of elitism. This meant that formalism, understood as an aesthetic rejection of the banal, was tenable only as long as there was self-consciously aristocratic or, at least, pseudo-aristocratic sponsorship of art. Around the mid-twentieth century the fashion-conscious decided to go slumming. Banality packaged as irony, the hot new commodity of the postmodern era, became the thing. At that point, formalism lost its luster, and the aestheticized banal debuted as the birth of the cool.