[lotsofpulp]

>Also why is it that the majority of the large tech companies are essentially marketplaces?

They may earn money from a marketplace, but the reason is not because they have a marketplace. They earn money because one they did or do something that others can't or were too late to, such as creating hardware and software people want, creating and operating online services people want (Maps, Cloud Services), infrastructure for retail, or a network where everyone is and can provide some level of proof for identity or credibility.