45% of SAHMs are in households earning 75k or more annually (2018 update).

And of that number, 2/3  are still in households earning 100k/yr or more.  Those numbers have been pretty stable over the last decade.  The percentage has gone up because there’s been a further decline in married parents while the total number of SAHMs was essentially unchanged from the earlier data.

Source: U.S. Census Bureau, Current Population Survey, 2018 Annual Social and Economic Supplement