1. I would like payment processors to have the resources and capacity to adapt to threats and maintain highly resilient infrastructure. This is expensive and requires a lot of ongoing investment.
2. If payment processing was turned into a public service, the complexity of international integration and necessary relationships, standards, etc. would become a public service burden. I'm not sure that I trust my provincial or federal government to handle this adeptly.
3. There is a lot to this that we're probably unaware of.
I'm not trying to protect banks in the slightest, but it's a baby and bathwater situation. I'm not confident in my country's ability to create its own payment processing platform that I would trust to be a reliable, sustainable, value-generating system operated by public servants. I don't mean value-generating in the profiteering sense, but in the "this is worth operating on public funds because, ultimately, it is more than worth what tax payers put into it".
I think some things are an awesome fit for public services, but a lot of places are probably not equipped to take this kind of task on safely and competently. My country is more likely capable of regulating these institutions, not replacing them internally.
We tried to make a COVID-tracking app and spent $59.5 million, and it was an abject failure. How much would we spend on a broken payment processing platform?