Speculative comment: if the product is advertising, then Google and Facebook have cornered that market and it looks like search and personal social network advertising could be natural monopolies. So there won’t be more Google’s, because there are already two and that’s what the market can support.

If that’s true the only way to generate Google-like companies (in terms of innovation) is to find a different business model, which means both founders and investors have to be more open minded, more patient, and more brave. That’s your first problem.

Probably the best alternative I can see is to charge individuals very small subscriptions for valuable products, but to make it at scale. Say you have 100m users and charge < 1 dollar each per month or even per year, and then you keep building new products using the great team that built the first one. Why hasn’t this happened? See above.