Unless there are more than 20 million millionaires, you're talking about the top 6 percent of the wealth distribution. I wouldn't call that particular percentile "barely middle class". That term probably should be reserved for the 60th percentile, no? Middle being 60 to 40? 70 to 30?
Edit: fixed my percentile thanks to child comment!
Inflation. Being a millionaire or having a six figure salaries used to have much more weight during the 80s.
Pretty much any senior level engineer at FANG can be a millionaire if they saved, but they can barely afford a standalone home in San Francisco. What does the term 'middle class' even mean if they can't afford a home?
Only 20% of millionaires surveyed feel they're rich.
Senior-level engineers at a FAANGs are already a pretty rare and prestigious class of people. I'm a reasonably intelligent person and I've failed to pass the hiring bar at every FAANG.
And of course they don't "feel" rich. Lifestyle inflation is a thing. Trade the Civic for a Tesla; send the kids to private school; buy organic groceries; take international vacations every year or so; yet still find the means to save more money each year than the average household in the USA earns. Feeling is a state of mind, not a state of being.
You're including non-adults (330m population @ 6%). It's closer to 8% of the adult US population. Not very many people under 18 are millionaires or reasonably likely to be. The non-adults in question fall under the millionaire household grouping.
And if anyone is interested in the household wealth distribution (as of 1Q21):
Edit: fixed my percentile thanks to child comment!