Rodman's two-year stretch with the Spurs can best be described as a trade value decline campaign, which ended with Chicago snagging him for a historically low price (straight-up swap for Will Perdue) and him becoming the crucial part of the 90s Bulls' second three-peat.
Rodman's erratic off-court behavior, his destructiveness to a team perspective, the fact that Gregg Popovich - the Spurs GM at the time - supposedly didn't like him at all, plus the personality discrepancy between him and the team's superstar player David Robinson ultimately made Dennis' two-year experiment in San Antonio a failure.
Dennis is a complicated guy. I think because of his background, he doesn’t always know how to express himself.
David Robinson, Bulls Talk Podcast
But despite things not working out well between Rodman and San Antonio, he did make a season-long impact the Spurs fans can remember him for. During the 94/95 season, Rodman made the All-NBA Third Team, despite only playing in 49 games, and starting in just 26. The Worm finished the season averaging 7.1 points, league-leading 16.8 rebounds, and 2 assists per game while leading his team to a record of 40-9 - a 67-win pace.
Rodman was suspended for the start of the season, for a combination of missing a team bus and team meeting and throwing a bag of ice at then-coach Bob Hill. He made his season debut on December 12 against the Washington Bullets, and 43 games later was forced to miss another month of regular-season games due to a separated shoulder after a motorcycle crash. Dennis was back for the Spurs playoff push and had played a big role in their WCF run, but San Antonio eventually fell short to future champions in Houston Rockets.
Thus Rodman's tenure with the Spurs came to an end. A tenure that could've lasted much longer. But the off-court stuff, and all the baggage that came with having Dennis on the team, overshadowed the impact he had on the court. So it ended up not being worth it for the Spurs. The Chicago Bulls can't say the same thing.