A very good question. Taking Thailand as an example, from season 3 until season 8, there were basically 4 teams that even remotely seemed to "play" the game, i.e. set scrimmages, change tactics, spend money on the TL. The last two seasons we have season a quantum leap in the number and quality of teams interested in improving. I am not saying that they are competitive yet, but it seems like we have 12 managers that care. According to bb-stats.org we have 45 users, 8 of whom I recognize from season 3. There have probably been 100 people sign up total. So using some fuzzy math I am guessing that the number to make a "stable" community is around 300-350 (1 in 10 managers caring enough to stick to it and become competitive). It could be possible to only have 32 users and have 32 active teams, but it would still take at least 300-350 people to try the game to get those 32 active managers. Of course, this number must be amended to account for a particular country's basketball culture. So maybe Thailand is more like 3000 users to get 32 active ones.
Once I scored a basket that still makes me laugh.