Okay...did they statistically control for the fact that a large part of those helpful-to-parents young unmarrieds are doing the dishes and taking out the trash because they still live with their parents?
Also, did they control for the navel-gazing tendencies of current American cultural schemes? We paint marriage as if it were the ultimate in self-fulfillment instead of the covenantally blessed bedrock for child-rearing that God intended it. No wonder such self-serving marriages (many of which end in "no-fault" divorce) fails to create community. It's inwardly focused in the first place!
(No...I'm not slamming on childless couples. Mohler does enough of that.)