I don’t feel like classic BB was particularly staged back in the day either (not in these sense of a programme like Love Island or MAFS)
They just selected the right group of people (like PP says to bounce off each-other), personalities that would clash, the right number of single people to make sure a couple or two formed etc etc
So drama would naturally unfold and BB could easily manipulate things through tasks, limiting food, providing excess alcohol, nominations and lots of other ways.
I wonder whether lots of the old-time contestants would pass the stability checks now