While the Businesses of those 3 giant companies are just operating in limited jurisdictions.
But, we can still able to buy US's company stock even we're not an American, I'm not sure in your country, but in my country I can use local broker to buy US's company stock. Although it's true Bitcoin is more widely since no one can stop people to own Bitcoin.
It will be impossible for centralized bank to have higher market cap than Bitcoin because gradually fiat is depreciating and bitcoin value appreciates, which is giving people more confidence to invest in bitcoin and abandon fiat because of lack of confidence in fiat. Banks are run by individuals but bitcoin is decentralized.
If most people think like this, those three banks would be bankrupt or they have very low market cap.