Why do we need my bank to send money to your bank via Visa or the Federal Reserve or any such thing, instead of having my bank send money directly to your bank? All they need to do is both support the same openly specified protocol for transferring money.
It's not something irreplaceable but it's not trivial either.
It seems like the primary thing they actually do is currency conversion, which a) isn't strictly required (e.g. plenty of small US merchants might hardly notice if they only accepted payment in US dollars), and b) could just as easily be transparently provided as an optional service by either of the card issuing bank or the merchant bank for cardholders or merchants who expect a non-trivial number of foreign currency transactions.
From NETs in singapore to girocard in Germany, Alipay to UPI.
Singaporean here. NETS is a shitshow of a dinosaur trying to stay relevant. They started as more of a debit card system like EFTPOS [1], but now lean more into merchant acceptance for both credit cards and QR codes. (Singapore is huge about credit card rewards, so few people want to use a debit card with PIN entry and no rewards these days.)
I think the problem with them, and many companies that focus solely on a tiny market like Singapore, is that their organisations tend to be full of comfortable dinosaurs that don't stay up to date with financial software engineering practices (I've lost money from government site transactions that were a hassle to get back), and there's a captive market because of their duopoly.
The biggest reasons they still exist are because they're a joint venture between the big 3 local banks, and our government likes their initiatives to have some competition to emulate a free market.
Pix, from its Wikipedia page, sounds like a bank account aliasing system, just like PayNow in Singapore.