It's mostly just the way things turned out without government intervention.

American Express' card started in 1958, as a pivot of their then already 100-year-old business: https://en.wikipedia.org/wiki/American_Express#1920s%E2%80%9...

Visa also in 1958 as a Bank of America (and friends) card, which quietly expanded into the mid-60s: https://en.m.wikipedia.org/wiki/Visa_Inc.#History

Mastercard in the mid-60s from banks who BoA wouldn't invite into the Visa clubhouse: https://en.wikipedia.org/wiki/Mastercard#History

And Discover in the mid-80s because Sears was big enough to be its own financial services firm: https://en.m.wikipedia.org/wiki/Discover_Card#History