Well, only because one of the household did a huge amount of unpaid labor. A lot of which now has been replaced with paid labor (child care, restaurants, house cleaners, and so on).
I meant it's been true forever that people with partners generally have a financial advantage over single people. (Even if they're not in a two-income household.)
What has changed is that dual income became the norm, and is no longer an advantage, but mandatory to compete on the housing market.
When single income was the norm, the norm was to put a family of 6 in an 800-1200 sq ft residence. That's still roughly equivalently affordable today.