Certainly isn't returns. Over the last 10 years, housing in the US has appreciated on average 39%, or 3.4% annually (https://fred.stlouisfed.org/series/CSUSHPINSA). Over the exact same time period, the S&P 500 with reinvested dividends has gone up ~323%. or 15.5% annually (https://dqydj.com/sp-500-return-calculator/).

To avoid cherry-picking, if we go out to 20 years housing has an average annual return of 4%, and the S&P 500 is at 6%. Go out 30 years and housing hits 5% while the S&P is at 10%.

PS, I really appreciate the Case-Schiller index used above for housing prices. It's methodology specifically targets the change in value of a house, instead of capturing overall price increases caused by house flipping, the expanding size of houses over time, etc.