Solved

Full elite= slow fill rookie

What is with the lack of people now joining rookie league? I was easily kicking 2 inactives a day from rookie when my league first started out. We're now doing well in our 11th season. We have a, more or less, full elite league. Almost the instant that elite hit 14 teams, rookie is lucky to get 3 or 4 new teams a week! I'm worried If it carries on like this it'll slowly kill my league off. Is it people choosing to not join or is there some algorithm that's slowing the recruiting down? I find it odd that it slowed at the time elite filled...any advice would be grand ??

Yeah i have noticed the sake in my leauge but we have nobody joining in the last weeek or so and even though im not the host i am still worried about it

It is concerning.  It's happened since last year, and it seemed like there was a temporary "fix" for it but now there seems to be a lack of players joining the leagues once again.  Sadly.  Our league shrunk significantly for a while, but then got back to how it used to be in the past - although I fear that we might suffer from a lack of rookies/pros again.  I think they'll find a solution for it

There are just too many leagues and not enough players to fill them. New players use the search function, this gives a very limited supply of leagues to join, if none match there requirements they think of starting there own. Even advertising in the forum is poinltess as new players dont even know about that function at the start. 
The rookie class is the life blood of leagues, there needs to be a constant supply of new players as only a few percent will actually keep playing.
Once a league starts to lose players its very hard to rebuild as players want to race and won't join a league with very few players in it.
There are numerous leagues with half a dozen or so players, restrict people from opening leagues until they have reached a certain level, this proves they are serious about the game.

This restriction can be considered as league rule I suppose?

Hosts should have more power with the promotion and relegation in their league. The whole tier system needs revamped but if hosts could control the teams going up and down, you will probably find a lot would choose to empty their rookie league and this would bulk up other Rookie leagues in other leagues with people who are actually playing. It’s not like we are going to run out of leagues anytime soon, we just need the system to be brought up to date to suit the numbers of active players at different levels 

Imo the recent influx in rookie was caused by lockdown in several countries. Now lockdown is eased, less new players try the game. 

Also, interest in F1 in general is not a contstant thing, i think it will pick up when real F1 season starts again. Rookies will start appearing by then.

But the influx we saw in last months was exceptional, i don’t think we will see that again.

I'm glad it's not just me then. Some valid points made as well. Thanks all