If you want to start a capital-intensive business like Google Inc or SpaceX, you have to use the typical corporate structure because you need the $X million in investments from angels, VCs, and the stock market.
The typical employees don't have a million dollars in their bank accounts to pool together and launch a Google-sized business as a co-op. The enormous costs for rack servers and data centers to scale out would outpace the employees' tiny cash contributions.