Formally structured systems are good at detecting easy / obvious cases.

The ones that get through are by definition the more subtle or rare cases.

For example a phone tree often isn't helpful because it tells you info you can find online.

But assuming you are capable of using the web site and did before calling, what you're usually calling about is exceptions to the rules.

The exceptions in a system are the things that matter the most.

LLMs are great at looking at in-sample things. But things that are out of sample are the exception!