Unfortunately, the MSMA (and all racing manufacturers in general) have decided that innovations should be extraordinarily expensive. In defense of the manufacturers, the sanctioning officials started this mess by trying to slow down the cars with methods that proved to be quite expensive. Engine displacement and engine induction regulations, for instance, have been very expensive regulations. In MotoGP, displacement regs eventually led to cylinder limitations. This is part of the post-war era in which manufacturers fight one another in the rulebooks and in the bankers' offices. The sanctioning bodies get fed up with the chicanery of skewing the rules to favor particular competitors. The sanctioning officials eventually decide that technology is evil. Enter NASCAR spec-racing, balance of performance, or stringent FIA technical regulations and homologation papers.
Besides the fans, no one wants innovation. That's why it never happens. Innovation won't happen until people actually do vote with their remotes. The manufacturers will cry about the lack of cheap media opportunities, and someone will have to come up with a new sanctioning model. In the grand scheme, we MotoGP fans still have it pretty good on the technical front, and to be honest, I don't really trust the fans to define technological advancement. Too many people are interested in Star Wars toys, and not enough people are interested in production-relevant innovation.
I don't see power density for naturally aspirated engines as much of a technology, and the manufacturers don't really care either. Been there and done that in F1. Not much to see. Engineers hit sonic airflow issues, and then they start shoveling hundreds of millions into the development furnace to create a technology that is only pertinent in a world with limited displacement. No such world exists. Piston speed and cylinder pressure are much more interesting technologies, imo. I'm more disturbed with the lack of direct injection than the low power-density of modern GP engines.