The league may not care about ratings, but the networks do. If they're going to continue to dole out the big bucks to the league, they better be allowed to use the match ups they think will draw fan interest.
The networks will decide which match ups give them the most exposure for the advertising dollars they're bringing in to offset that huge pay day they give the NBA. It may be a "mutually agreed upon" arrangement, but let's face it. Money talks.
LA and NY are the two big markets for the NBA. Not certain what the entire pecking order is, but I'd guess a lot of it is concentrated in the Northeastern corridor.