Ilia doesn't deserve to fight for the BMF yet. I know BMF is just a stupid toy belt etc. but if we were to take it semi-seriously, all BMF holders and challengers so far have been:
VETS who are known for violence. Not only can they do damage, they can TAKE damage, be the nail. They are proven durable tough guys who can fight through adversity, bounce back from losses, not just once or twice but consistently throughout long gruelling careers.
Khabib and GSP were great fighters and winners but not BMF's. GSP had a boring non-violent style and Khabib never showed he could be the nail and bounce back from a loss.
Right now Topuria is building a reputation as a BMF because of his violent style but he still isn't a proven tough guy like Max, Justin, Dustin, Masvidal and Diaz. He needs more mileage.