The most current levels per gdreports have D1 at their 3rd highest level in the past 11 seasons, D1AA at their 3rd highest, D2 at the 6th highest, and D3 at the lowest level in 11 seasons. Overall we are sitting at the 6th highest number of teams out of the past 11 seasons. The prior season totals for all worlds combined was the 2nd highest overall in the last 11 seasons, with the most number of coaches in 1A and 1AA over that period.
It looks like the normal post-football fall off, but the low number of D3 coaches could be concerning for the future.
The hard part is that there is some tipping point where people don't stay. If you are a human manager in D2 and you have played a few seasons and haven't made the playoffs...you probably aren't going to enjoy the game too much. Plus recruiting gets more frustrating the more humans are in a league. I think if they combined leagues, people would drop out and the leagues would return to historic sizes.