Greed, plain and simple. After that is the simple lack of decentralized organization. Centralized corporations are hard enough to organize. Setting up an effective DAO is an absolute nightmare.
One of these days someone will come out when some bad ass template for making a good DAO, but until then governance is being tinkered with by hand in a custom way, and because of greed, that tinkering puts the tinkerers in charge.
Once someone creates an organizational structure that is more fair and can guarantee hard work won't be overlooked, the floodgates will open.
It's also a matter of learning to decentralize development. How do we come up with a system to pay devs to complete small portions of a large project. I can see with the proposal system we are already working toward this goal. Baby steps.