I'm an IT guy. I know that transaction takes milliseconds to process.
And like a typical IT guy, what you "know" is beyond question. No way you could possibly be wrong.
If, someday, you work with enterprise systems, you might come to realize that very large systems are often riddled with inefficiencies. When multiple parties are involved, or legal compliance, those inefficiencies can become powerfully entrenched.
Take a look at some of the high rated comments on this article for explanations as to why and how banking is not as efficient as you imagine.