What we have now is either people staying single longer and eventually they end up with Simpsons' style living standard (while staying Single) or they eventually achieve it via DINK lifestyle.
I think a huge part that has played into making this transformation is due to people's increased access to cheap loans (mortgage) and the idea that real-estate is the ultimate ROI game-in-the-town and the new pension fund.
What we see now (compared to say 1980s): almost no major corps offering pension, inflation to the point where both Husband and Wife need to work in order to just afford a property and perhaps a kid, creeping fees/charges (cellphones, internet, netflix, disney+, etc.).
This all leads to people, in my opinion, to look for safety net in order to fend themselves in old age: buy house -- no, make it 2 or 3 houses so you can live off their rent income, delay (or forget about) having kid(s) to achieve that financial goals. Automation and globalization has also caused some pain points: IT jobs are much more competitive than say even 10 years ago and there is always threat of being left out in the cold due to outsourcing.
See, funny thing is, here in Canada, I would always see hardworking immigrant families where the Husband and the Wife would be working in multiple low-income jobs and even their teenage kids would be picking up retail/factory job while studying to balance their family's financial books. To me, it always seemed excessive or even mindboggling - but now, it makes perfect sense...it is the very future for the masses in North America.
And for folks in developing World: Don't worry, your turn will come to experience all this (if you haven't yet) soon enough in your lifetime. I guarantee it.