They are victims of their own system. They don't do poorly enough to convince fans that they don't have the talent needed to win. Their streak of 50 win seasons stretches over two decades. For this reason, their bar for "need to rebuild" isn't at the bottom of the standings like a Philly or Phoenix. Their's is at the bottom of the playoff seeding, or thereabouts.
When David was injured, the Spurs did so poorly they grabbed a 1st overall and Tim Duncan. They haven't been back there since. The system they use means they likely won't be back there until Gregg retires. Kawhi was the bridge to the next successful streak, however he might have other ideas. Not everyone who is quiet wants to be part of a small market franchise vs large one.