The supporting cast hasn't been championship-level
Through the first few weeks of the season, the Golden State Warriors' supporting cast has been everything but championship-level. Stephen Curry is averaging 30 points per game but the team's second-leading scorer is averaging just 15 points per game. The team's fourth-leading scorer is Jonathan Kuminga. In the past, the reason why the Warriors have been so dangerous and dynamic was due to the firepower that they had, especially on the offensive end.
Simply put, that is no longer the case for the Warriors. Klay Thompson and Draymond Green are both past their primes. Andrew Wiggins is on pace to have the worst season of his career thus far. Aside from Curry, there's simply not of ton to fear about this team. Certainly not on the offensive end.
I can't remember when the last time that was true about the Warriors. If something doesn't change quickly, even if the Warriors do make the playoffs, there's not going to be much fear about them when it matters most. That's simply not a characteristic of championship contenders.