I have no idea about the frequency, but I have reason to suspect some are quite frivolous.
Like you, I believe it should be the last option. I'm just not sure that we are the majority.
It was a very different situation, however: someone had my CC info and loaded it onto a new account and made a large purchase.
Oddly when I inquired Amazon said they had already flagged the fraud and I needed to send a chargeback. It appeared that they were not going to proactively let me (or my cc company) about the issue.
I get it, but can't help but lose a little respect for a company that knows with certaintly one of their customers has been defrauded and sits back and waits for them to notice. Maybe they couldn't initiate the refund, but surely they could send a notice or otherwise reach out.
I'm kind of surprised I even caught the transactions given how many legit ones I have each month with them.