You have a shot clock in any BB game. You have to take a shot within the prescribed time or the ball goes over to the other team. Therefore, you only have three ways to keep from running up the score. You either don't take any shots and just play defense, you deliberately miss shots, or you slow the pace of the game and only take shots late on the shot clock.
The first two choices are not viable alternatives, particularly when you've inserted your second teamers. They deserve the chance to play the game normally. They don't get to play much so they want to do all the things that constitute playing BB. You also need to give them the experience of playing the game normally.
The best example I remember about it was a season many years ago when Teresa Grentz was coaching at Illinois. They had played Tennessee earlier that season and then played us. Both games were blowout losses, but after our game, when asked about the two lopsided losses, she said "Geno is a gentleman." It was a not-too-subtle dig at Pat Summit because she used a full court press right up until the last minute of their game against Illinois while ahead by over 50 points. Grentz didn't appreciate it. I recall Pat once defending her practice of doing that by saying she never stops working on things she thinks her team needs practice with, no matter what the score of the game is.