Because literally 85% of the entire league is irrelevant.
Saying 15% of the league is relevant right now is actually being more generous than the NBA deserves. The Warriors, Cavaliers and Rockets (since getting Chris Paul) are the only 3 teams that have any sort of chance to win this year's NBA title, and the Rockets are still a huge longshot.
That's 3 out of 30 teams relevant, meaning it's actually 90% of the league that doesn't mean shit. The Warriors and Cavs will run through everyone, the Rockets will be the only ones to put up any sort of a fight, and if you're not a fan of one of those teams, then good luck finding a reason to care about the NBA until at least the conference finals. The "arms race" mentality that the stars have is destroying the NBA from the inside.
I literally watched more hockey in the past year than basketball because it was so obvious that the finals would be Warriors vs. Cavs and I cared so little.