>Certainly no one can be an expert in everything, but regular audits from third parties of one's business at semi-regular intervals is prudent. We call in an external IT security auditor regularly ourselves to make sure we're not missing things and still following best practices.
You're absolutely correct, up to a point.
As an InfoSec professional, I've been on both sides of such audits. Sometimes they're quite good. Sometimes they're awful. Usually, they're somewhere in between.
What's more, just because an audit has been performed (even a really thorough one), there's no guarantee that the recommendations will be applied, or even if they are, that they will be applied competently.
Leaving that aside and assuming that everything is done properly and thoroughly, regardless of all that hard work, it just takes one non-technical resource to click one link, and ransomware could be loosed on your network.
There are, of course, mitigations and, hopefully they are all in place and just the one desktop/laptop system is compromised.
All that said, many organizations don't have the time, money or expertise to properly secure their environment, let alone bring in outside auditors.
Medium/large companies with such resources should absolutely do all of those things. But the vast majority of companies in the US are SMBs who likely don't have those resources.
I'm not making a value judgement either way about the value of mandatory reporting, but I don't agree with your assessment.
Edit: Fixed typo (word --> work).