The dream was that basketball would have a real minor league, where young players could develop without appearing only in garbage time, where teams could devote attention to youth without conceding victories. It wasn't going to happen overnight, and it didn't. But 12 years after its creation in 2001, the D-League is getting ever closer to meeting that mission.
To wit, there are currently 17 D-League teams. Fourteen of them are in single-affiliate agreements, either because they are owned outright by an NBA club or because they have a hybrid management relationship. That means that the 16 NBA clubs who don't have single-affiliate relationships share the three independent D-League clubs. The Iowa Energy and Bakersfield Jam each have five NBA clubs theoretically sending players down to them; the Ft. Wayne Mad Ants have six. The mere logistics makes it impossible for those NBA clubs to effectively use the D-League to the same advantage that the single-affiliates do. Not only do the sharing clubs have no say in D-League team management or coaching, they can't even be sure the player they send down will be among the five or six most worthy of playing time!
The single-affiliate teams can ensure their young players get playing time and practice in a system that will be familiar once they come back up to the NBA level. That's what a minor league should provide, similar to how reserve teams in the soccer world work: opportunity beyond mere practice, but better practice, too. Single-affiliate NBA teams can offer that. The other 16 clubs cannot.
As that advantage continues to grow, more of those 16 clubs will see the D-League as a valuable investment. However, there are so few clubs (three) available for partnerships. Which means ... expansion, and likely in the extended regions of those clubs looking to pick up teams.
It makes all kinds of sense to have your single-affiliate D-League club fairly close. You can send and retrieve players at lower cost and on tighter schedules, and you can connect with fans outside the core metro area you play in. An example would be the Golden State Warriors, who moved their D-League affiliate to Santa Cruz at the far southern tip of the Bay Area. The Cavaliers have a D-League club in Canton. The Celtics' affiliate is in Maine. The Texas teams have their affiliates in that same state, and the Thunder own the D-League club in Tulsa. You get the point.
There's still a lot of space between today's D-League and a true minor league. First of all, while teams can assign roster players to their affiliate, they don't hold rights on other players they add to those teams. The maximum NBA roster size is 15. Instead of devoting two or three spots to D-League players who aren't young first-round picks getting seasoning, teams usually keep veteran role players in those spots. Raising the maximum roster size to, say, 17, while maintaining the league's active roster limit would allow teams to pick a number of fringe NBA prospects to develop in the D-League.
What could slow that down? It wouldn't necessarily raise costs because aggregate NBA salaries are tied to a certain percentage of league revenue, but such a move could lead the NBA teams without single-affiliate agreements to feel as if they are being pressured to invest in the D-League, which could lead to opposition on those grounds. And a chunk of players could object, too: more players splitting that revenue means less money for everyone. Stars already give up a lot to mid-rung players. They'd be giving up a bit to low-level players as well.
But the writing's on the wall: the D-League is a success and it's on the way to meeting its goal. The NBA made the right decision by trying to create the second level of American pro basketball on its own instead of letting someone else do it, and it's now paying off.