But that's simply not true. It may be true in certain places. Two people probably can't realistically afford to buy in San Francisco, but it's big world out there. You don't have to live in San Francisco.
Not even in the 40s and 50s could you live anywhere you wanted, while owning a house on a sole income. Like today, the houses affordable to one income were only found in certain places and only those who were willing to move (or were lucky enough to have been born) where housing was affordable were able to own them.
From what I recall, the homeownership rate in the 1940s was only around 45%. Owning your home wasn't anywhere near as common as it is today. To say that people with one income could afford their home back then is simply cherry-picking those who could, ignoring everyone else.
Many earners are part-time earners nowadays. If you want to make that point, you may want to look at the median income for full-time jobs ($50k for men).