There has been a huge growth in BB, so you have a bunch of teams given 18 players, which is probably more than they can use. So they start going through the roster. In most cases, the older players aren't exceptionally better, so teams try to sell extra players, or fire them. If a player is 30 and not much better than someone who is 21, the older player will be transfer listed or fired.
Also the draft was just completed before most of the new teams joined BB, so you may have had 3x2000 young players drafted, and spread among 20,000 teams that is only 0.3 per team. In future seasons, this should be more balanced with a larger share of teams participating in the draft.