There are probably hundreds of thousands of credit card terminals installed in the US. The delta of potential improvement is small enough that there isn’t a huge motivation to change anything.
https://paylinedata.com/blog/regulated-debit-vs-unregulated-...
This cost is why we saw some retailers attempt to make their own wallets. A wallet app is a bit easier to integrate for the merchants than a new card network. The downside is that consumers don’t care about wallet apps. We want our credit card rewards!
Starbucks benefits because they only incur transaction fees for every (say) $25 pre-paid block, instead of for every $3 coffee. Swipe fees decrease as a percentage of revenue.
They reward consumers via their loyalty program.
They also incur benefits because money in hand and earning returns today for goods and services that will (maybe) be provided in the future is better than money received only at the point of sale.
AMEX/Discover can't even take over Visa/MC...