The US already has several debit card networks; debit cards are also required to be usable on at least two unaffiliated networks, so there's a requirement for options while charging a card. [1] However, debit card transactions are unpopular. Users would rather pay later than now, especially when dealing with fraud or returns; rewards credit cards are popular and merchants typically don't charge more for credit than debit, so the user gets a nominal dollar discount and a time value of money discount when using credit (otoh, the merchant also gets paid with a discount and paid in arrears).

Many of the interbank networks were formed by a consortium of banks, as was Interac; Mastercard was also formed this way (as Interbank).

[1] https://www.ecfr.gov/current/title-12/chapter-II/subchapter-...