Because the Pistons have retained the team that won a le and remained at a championship level, the Spurs have as well. The Lakers didn't. They have undergone a resurgence this year, but they have yet to prove they can win a le with their current group. I'm not saying they won't, outside of San Antonio and Detroit, they have as good a shot as anybody, but they broke up the team that won three les in a row.
Obviously the Lakers have a more storied franchise than Dallas, and most observers agree that the Lakers are slightly better than the Mavericks right now. But we still need to play the games later this spring.