The NBA had instituted a "hard" salary cap in the early 80's to try to bring some balance. The league was seriously at risk to contract from 22 teams down to about a dozen. (Who was losing money? Cavaliers, Bullets, Pacers, Hawks, Braves/Clippers, Nets, Nuggets, Spurs, KC Kings, Warriors, maybe more.)
Then the Celtics started whining that they couldn't afford to resign Bird, and the Bird rule was created so that the Celtics could circumvent the salary cap (thus making it the soft cap that we have today) and the NBA continued down its trend during the 80s were every October you could successfully pick the Western Conference champion (Lakers) and had a pretty good chance of picking the Eastern Conference finalists (Celtcs and generally either Philly or Milwaukee until Zeke and Dumars led the Pistons to respectability.)
The golden age of The Finals was also a 20-team race for fourth place, where those teams had no chance of cracking the top three.