He may have the votes, but the NBA Constitution does not address this type of private behavior. Adam Silver is going to lose in the end.
He probably figures that it's more profitable to deal with Sterling's probable lawsuit in the offseason than to deal with a boycott by racist players now.
Owners of pro leagues don’t let the appointed commissioners boss the owners, it usually is the other way around. They don’t let the guy have veto power over the owners.