Solved

Why only for Pro and Elite?!!?

I totally disagree with limiting the league rules to Pro and Elite.
with an account I am in a private league with my friends and we are all in rookie because promotions are disabled.
So we can't use the new rules just because we're on the rookie? it's not right!
at  least you should re-enable manual promotions for private leagues.

I think no refueling should be default of Rookie. Because it's a very common error of new managers to over-fuel or run out of fuel. With more experienced managers in Pro and Elite refueling should be optional in those leagues only.  But not sure why Rookie mangers are forced manage refueling.

 I think it's because fuel burn/weight isn't regulated to be the same for all cars that this made having no refueling in the rookie Tier. Thus devs are basically forced to disable it for Rookie as it would impact the weight of those cars far too much! Another reason why fuel economy should be the same for everyone when "no refueling" is enabled. 

Then Rookie managers can enjoy having less to manage in those leagues who enable it. 

Rookies are learning the game, let them learn to manage live race before dumping league rules on them, that I think is the reasoning behind it

Disable for Rookies only as stated. 

By the amount of abandoned Rookie accounts and watching rookie managers who chronically over-fuel for their stints. It seems logical to as least have some leagues more noob-friendly. 

I don't see how disabling refueling for Rookies affects established players like yourself. But my view has been I use and enjoy whatever the game has... at least until another game capitalizes on missed opportunities. 

I can enjoy the game either way and do continue to look forward to races. 

I’m not a big fan of no refuelling rule, but if you remove it how will rookies ever learn how to fuel their car efficiently?

Well, pretty much the same way many people learned to ride a bike with training wheels. When they have a bit more experience with the many other management tasks of IGP (grateful it's so extensive and emersive), then they can opt to join a league with refueling enabled.