This.
The size of the market is not like border wall around any given city. It is also the surrounding area, and largely the state and general region. You better believe in Texas alone there are far more Spurs fans than there are Jazz fans in all of Utah/Wyoming/Idaho/Montana combined. Not to mention surrounding states and just the general popularity of the franchise around the country. The Spurs are undoubtedly more popular in general, thereby entertaining a much larger fan-base, than the Jazz, and therefore, worth more to the NBA in general.
This highly highly scientific study bears this out:
A revealing look at the 25 NBA teams with the largest social media fan bases on Facebook, capturing the pulse of basketball's most loyal and connected followings. These franchises dominate the digital game.
bolavip.com