This did not stop people in the past. You read of three-room New York tenements holding families of ten, or families with half a dozen children living in a single-room frontier cabin, and this was considered commonplace.
My parents raised eleven children in a typical four-bedroom suburban tract house.
I wonder why modern people would be different?
Because we have an expectation for more space. Pretty simple, no one wants to go backwards to when we lived in single room tenements with a wife pumping out babies for a decade in a row. Also, no one can afford a four bedroom home with twelve occupants on a single income like in the 50s.
You couldn't in the 50s either. You just made do.
That’s the real key to all this - if you want it, you make do, and learn to grab what you can.
Much worse than housing is the vehicle when you cross the 5 or 6 kid boundary, your available vehicles begin to rapidly plummet.
They didn't have birth control then so it was much less of a choice.
Well, then we should say that it is something related to availability of birth control which has caused the change, not some novel preference for living space.