How Did Marriage Become a Mark of Privilege?

currently, 26% of the poor adults (age 18-55) , 39% of working class adults, and 56% of middle and upper class adults are married

in 1990, the 3 numbers were 51%, %57, %65 respectively.

and while marriage has declined a lot, the childbearing has not. this means there are lot more children without both parents caring for them

Perhaps, in the aggregate, those with more assets are more highly-educated about money and feel the need for marriage to consolidate expenses and protect their estates?

Or perhaps those with fewer assets feel that they don't have enough money to raise a family. Incidental kids are outside of that equation for them, though.

or, both, and some more