I read in the Game Manual that Local Players (with Talent, of course) bring more fans, along with Players on the National Team. Now, to win, you may need to grab that Serbian Center for your USA Team (I'm trying it to get an early Winning Advantage right now, hope I land him, though meeting the Salary will be tough)... and the Wins will help fill the seats. However, not having any Local Talent will hurt, since I'll basically be riding the Serb as far as we can go so he'll be the focus getting all the Awards and such.
You built a nice squad, top of the leauge, but the fans haven't gone all Dallas Maverick and connected with the Foriegn players yet. I am not sure if this happens over time, like if you keep the guy for a few years and he becomes a Local Hero or such, or if he will never have the same draw as a Local Star, but being heavy on Outside Talents instead of Local could be why you are not selling out yet.
By the way, teams like the Mavericks and the Spurs, who both have a high density of Foriegn Players, still sell out, and some Foriegn Players have some of the best NBA Marketing in the League... so I'm not sure how much of a bias the game puts into something like that... but it may need to be looked at again and re-tooled.