I'm not sure things are much different today vs back then. Two working parents were always the norm, even in the mythical 50/60s.
https://www.pewresearch.org/ft_dual-income-households-1960-2...
Prior to that most households were single income.
For example, these days said couples tend to be older, more educated and with less kids on average. Which may explain why they're more likely to be dual income. You don't have time for a second job when you have 5 kids to raise. But that's less likely to happen today, statistically speaking.
So your comparison most likely compares people in different stages of life, not the same people across generations.
But in any case, the worker participation rate has stayed between 58% to 68% over the last 70 years, with around 63% today. Doesn't sounds that big of a difference to me.