there's over 20 million millionaires in the USA, that's like, what, 1 in 20?
Housing is actually quite liquid as it is incredibly easy to mortgage. More likely you are overestimating how much housing value is actually there. The majority of American homeowners have already tapped into that liquidity. Owning a house that is worth, say, $1MM on the open market doesn't necessarily mean that your net worth is $1MM.
There is a huge difference between someone with a net worth of 1M (owns a small home, still needs to work for a living) and a net worth of 30M (can get more than 1M per year of capital revenue without working).
And I'm not even talking about billionaires.
Typically, it would seem that is indeed the case from most calculations I've seen. I mean, are you really worth a million dollars if you have to be homeless to access those dollars?