The issue is not only complexity, though it does play a role. You can also run into issues with pure text parsing, especially when whitespace is involved. The IP thing is a very classic example in my opinion, and while whitespace might not be an issue there (more common with filenames), the queries you find online in my opinion aren't less complex.

Normal CLI output is often meant to be consumed by humans, so the data presentation requirements are different. Then you find out that an assumption you made isn't true (e.g. due to LANG indicating a non-English language) and suddenly your matching rules don't fit.

There are just a lot of pitfalls that can make things go subtly wrong, which is why parsing general CLI output that's not intended to be parsed is often advised against. It doesn't mean that it will go wrong.

Regarding Python, I think it has a place when you do what I'd call data set processing, while what I talk about is shell plumbing. They can both use JSON, but the tools are probably not the same.