Earlier quoted context omitted.
The major cloud providers all aim for 99.999% uptime. Keep in mind that 99.99% uptime means ~4 minutes of downtime a month. I think there are other reasons that banks may not want or have the ability to run their core services on the cloud.
Let's be honest, it's Azure. The only reason you choose it is because either you compete with Amazon in some way, or you hate your infrastructure engineers, or don't know better.
I think Azure is cheaper for certain workloads as well, and at one point had DCs in places where AWS didn't. But it's mostly the "we already buy X Microsoft product, and they cost about the same, so..."