I read through a lot of various transaction logs from various financial and other systems. It's really easy to make assumptions,mistakes and underestimate the complexity of business and real world environments.

I think it was the hubris of the "modern" management of the bank to think they could replace a complex system that had grown organically over decades and had probably lost most of it's institutional memory in the form of retirements. It's the same mentality that brings us the insecure IoT and folks thinking that JavaScript programs with hundreds of externally managed dependencies can be "secure".

We know how to build good, secure and real time software. We have quality modern languages and best practices that the industry ignores. Instead, we would rather have fast, insecure hardware and the latest fashionable framework. We are still tool using primates.