I think most folks have only the haziest understanding of how to fund retirement, and how much they'll need. So if $2 million is a rule-of-thumb number they've heard for most people, then surely $10 million would feel safe.
But that's based on gut feelings, comparisons with things some guy said in a pub, and fear of being old, vulnerable, broke, and homeless. I know because that was me a decade ago. It's not rocket science to look at how much you've spent over the last few years and estimate your future spending needs, nor to read some FIRE articles about asset allocation, investment options, and typical historical market performance, but that's all really scary stuff when you're starting out. I've seen smart friends' eyes glaze over with fear and avoidance when I bring it up.
So I do think $10 million is more than enough to live well indefinitely, but I understand why so many people aren't convinced. It's emotion, not logic. And it's a bet you can't afford to get wrong, so might as well err on the generous side.