That would be difficult to do, if say all banks decide to only support Windows/MacOs. My bank that I use is a bit wonky on Firefox but works fine on Chrome. Some banks even refuse to run on Firefox. Also, switching banks might be more difficult than switching an OS. And you would lose the reward points if any if you switch a bank, not to mention, if you use autopay that is configured to withdraw from a certain card, you would need to go and reconfigure that everywhere.

It is not technically impossible, it's just going to arduous.

There are already countries where all banks in the country (and often it is a mere handful; not everywhere is like the USA with a big choice of banks) already require e.g. using their app on an Android version that passes SafetyNet, in order to log in to online banking.

Or ultimately fund your own if all banks adopt this under a regulatory recommendation.

I just believe that imposing this cost and inconvenience on Linux users (in this example) would be a bad thing.

Are you going to make your own bank too when enough banks do it?

Does that seem easier for people to do than buying a Windows or MacOS device? If your oldest credit cards are through your bank it could wreck your FICO for quite a while.