the marketing!
I know I will be cursed, booed, spit on and generally carried out on a rail after being dipped in oil and feathers, but i work in marketing.
The need for large entities in the business will still be there since marketing costs a lot of money. Sure you can self-publish a game but it will almost certainly drown in the flood of games that are released. A bad game with marketing will almost always outsell a good one with no marketing. The almost part will always be the luck factor.