In addition to what bendbro suggests, which is actually quite close to reality if oversimplified, banks also have sovereignty concerns with data that may have a

In addition to what bendbro suggests, which is actually quite close to reality if oversimplified, banks also have sovereignty concerns with data that may have additional classification and regulatory strings attached. In Australia where I’m based, ‘material’ data such as financial and audit information must be kept in country and its veracity attested to, which is why so many large banks here at least still have big iron in managed data centres for most of their core transactional systems. Edited to specify which sibling I was referring to.