You mean like this:
In previous eras, teams had ZERO players behind the 3-point line because teams didn't shoot 3-pointers - in 1985, teams averaged two attempts per game, compared to 22 per game today.
So the setup above is characteristic of TODAY'S game, not previous eras - you never saw the above setup in previous eras.
Coaches were actually quite dumb in previous eras - not only did they not space the floor, but their approach of positioning offensive players inside the 3-point line and closer to the rim activated the legal paint-camping provision stipulated in
Rule 2b of the Illegal Defense Guidelines - this rule allowed defenders to paint-camp with no time restriction if their man was in the paint already, or within 3 feet of either side.