Well the main thing is the concentration of capital. Guys like Jeff Bezos aren't interested in founding cooperatively-owned companies, and they have all of the money. Add in the fact that average people are very strongly atomized and prevented from forming stable social bonds, and the likelihood that you'll get a cadre of people together who want to start a cooperative business and can also afford to do so is very, very low.

That said, the few coops that manage to exist are often the best places in their industry to work, precisely because the profits are shared more equally than in the more common private or publicly traded corporations.