Let's dispel some myths first. Google and Facebook are not technological companies; they are media companies not unlike CNN or The New York Times. While Google and Facebook employ some fancy technology they are not in the business of selling this technology to others but they use it solely as a mean to captivate an audience just like CNN is using television technology and The New York Times is using printing press. The business of a media company is to sell attention of the audience they have captivated through their content and that's exactly what Google and Facebook do.
Selling technology is hard and not very profitable in the long run. Even though your technology is supporting businesses processing billions of dollars there's no actual need for you to have any share of it beyond the fixed price of your technology. Let's take a money counter as an extreme example. Even though money counters process billions of dollars each day they cost just a few hundreds dollars each and the total market for money counters is probably on the order of hundred million dollars. While producers of money counters would definitely prefer to take a share of the money their machines are counting, no customer would be willing to accept such business model now since competition took care long ago that non-optimal business models for selling money counters were rooted out.
If you're building a technology company you might have lots of fun doing it, but you won't make your investors happy. So better start contemplating now what services you can build on top of your technology or brace yourself for a race towards zero.