That was actually something the owners pushed for and got. The players agreed to it because there are a lot more second and third tier guys who would be making a lot more money than first tier guys who were getting paid less.
This article is a few years old but it does a good job explaining how it somewhat backfired on the owners.
https://www.cbssports.com/nba/news/max-money-explained-for-every-anthony-davis-theres-a-greg-monroe/
The max contract -- and especially the super-max, starting at 30 percent of the salary cap for high achievers -- was conceived for players exactly like [Anthony] Davis.
The problem is, outside the rarified air where Davis and other top-shelf superstars live, the NBA's max contract has become so common and overused as to completely lose its value and meaning. And critics say it's actually had the opposite effect than what owners intended when they pushed for it during the ugly 1998-99 lockout that cost owners and players hundreds of millions and canceled the All-Star Game.
"When you place an artificial bottleneck, you're going to create disequilibrium," agent David Falk, who represented the NBA's first $30 million-a-year player, Michael Jordan, told CBSSports.com.
"By saving $20 million on the best five players, you're probably paying 30 guys an extra $10 million each. If the owners realized that by saving $100 million it would cost them $300 million, do you think they would've done it?"