What's stopping a large, profitable company like Valve from starting its own payment processor? Surely the technology part of it can't be an impossible hurdle.
If you believe Steam et al, the payment processors are bowing to the card networks in this. So being a payment processor wouldn’t help. You need to sidestep the networks. In the US that means either dealing with ACH at scale, which is a challenge, building a new card networks (which is hard) or only using alternative payment methods such as bnpl or crypto. Each of those will limit your buyers, which as a merchant is…
Which is why someone has big interest in keeping it this way as in Europe practically every country solved this issue a long time ago and people do daily shopping completely omitting Visa/Mastercard. They try to fight back without much success.