If that were the case they would have done it already. This isn't a problem of technical feasibility (they most definitely can support it technically); it's a problem of legal and regulatory feasibility within the existing banking system that leads to high costs on their end, and it's hard to roll back policy. You can even see it now with Visa partnering with Coinbase, Fold, USDC, etc.; they just can't operate within the bounds of the existing regulatory environment to support instant micropayment systems. These companies have to branch out into "crypto" and Bitcoin to compete.

Maybe they haven't done it yet because there's too little demand. Easy to get around regulations if you have armies of lawyers and lobbyists.