Why does fleet footwork going to scale with crit?

I thought the whole reason it was changed from warlord's bloodlust was so other classes could make use of the of keystone. Since it scales on crit only ADCs will have the most beneficiary. ADCs already have so much survivalbility from the shields and heals that the supports provide. Ex: locket, face of the mountain, redemption, locket, knights vow. This mastery basically gives ADCs free lifesteal stats without having to purchase lifesteal items and lets them reach their powerspikes way sooner.