The driver is supply & demand. Lots of people can & want to find a proven product that sells and compete on quality or price. When they do this, it drives the price down, and it continues to drive the price down until each of these firms is making just barely above what they would taking a job commensurate with their skills.
The economic returns from startups come from them having a monopoly on their particular good or service when it turns out that people want it. If they do nothing, eventually competition will drive their returns down to nothing as well. But because they were working on a hard problem that most people thought was useless, they have a head start that they can use to build a lead that discourages competitors from entering the market. Nobody sane competes head-to-head with Google or Facebook, because they managed to get such a head start that you'll probably run out of money long before you can catch up to their offering.
My widget is more expensive and, wait for it, less reliable!