Why was there a lockout during the 1998-1999 NBA season?

Context: The 1998–99 NBA season was the Hawks' 50th season in the National Basketball Association, and 31st season in Atlanta. On March 23, 1998, the owners of all 29 NBA teams voted 27–2 to reopen the league's collective bargaining agreement, seeking changes to the league's salary cap system, and a ceiling on individual player salaries. The National Basketball Players Association opposed to the owners' plan, and wanted raises for players who earned the league's minimum salary. After both sides failed to reach an agreement, the owners called for a lockout, which began on July 1, 1998, putting a hold on all team trades, free agent signings and training camp workouts, and cancelling many NBA regular season and preseason games. Due to the lockout, the NBA All-Star Game, which was scheduled to be played in Philadelphia on February 14, 1999, was also cancelled. However, on January 6, 1999, NBA commissioner David Stern, and NBPA director Billy Hunter finally reached an agreement to end the lockout. The deal was approved by both the players and owners, and was signed on January 20, ending the lockout after 204 days. The regular season began on February 5, and was cut short to just 50 games instead of the regular 82-game schedule

Answer: The players and owners failed to reach an agreement on salaries.