Why don’t we have 2 lines like hockey does? It would keep all the players ‘happy’ as far as playing time goes. If a team is deep play them all and wear out the other teams. Kentucky use to do this back in the 90s.
A lot of reasons.
Conditioning- It is really tough to "wear out" other teams. Teams that have utilized it to some degree of effectiveness have been high pressure defenses. We play at a very slow pace, relatively speaking. High major athletes are extremely well conditioned these days, especially since so many of them are upper-classmen transfers. You are playing a lot of grown men, who won't necessarily hit a wall. If they do, it comes very late in the game. It often might be too late to make a difference
Continuity- Familiarity with the guys you are sharing the court with is vitally important. Sure, being on the court with the same group all the time would, in theory, help that, but its a long season and players are going to miss time.
Matchups- The rise of analytics has led to a LOT of matchup hunting and lineup tinkering to exploit certain mismatches. When you have set platoons, you limit your ability to take advantage of these things. We know how driven our coaches are by the numbers and matchups... they'd never paint themselves in a corner in this way.
Most importantly, you are limiting the amount of time you have your best 5 on the court. You either play your 5 best and then your next 5 best, creating stretches where you are likely to be over-matched, or you split up your best 5 and they don't play together.
Several coaches have tried it, they all eventually abandoned it.
To grue's point, Cal tried it the year he had 9 future NBA players. (14-15) He was trying to keep everyone happy. It kind of bit him in recruiting the next year, because a lot of guys want to play 30+ minutes. (4 top 20 recruits in 2014; 2 in 2015, while trying to replace 7 guys who were drafted. Fortunately for him, the #71 rated player that year, a Canadian kid, turned out to be pretty good...)
When asked after the 2014-15 season loss to Wisconsin in the Final 4 he said: "If you ask me if I'm ever going to platoon again, my answer is NO. Last season was an absolute outlier. It's just not the way I like to coach. I would rather play seven or eight guys because I believe that gives us the best chance to win. I think we wrote the book on platooning this year, but I hope we stick it on the shelf and never have to use it again."
He has tinkered with the idea again in subsequent years, occasionally doing a hockey style substitution in-game, but never embraced it as a primary strategy again.
