Music generally lacks innovation for the same reason why phones and men's clothing lack innovation. Most of the easy low-effort ways to be appealingly different have been discovered already. Music's creativity has been spurred by a series of technological innovations, the invention of the electric guitar, then the invention of synths, multitrack recording, drum machines, then computers with sampling, loops and DSP. It's been artistically transformed by blues, country, jazz, rock and roll, urban, dance and rap. Each one had its own series of innovations driven by creativity (doo-wop? math rock? new jack swing?) but the genres have settled into their mature phases. Probably some entirely new genre needs to come along and shake things up, but that's hard. Until then we'll continue to get the artistic equivalent of a new coat of paint every few years.