instead of picking 2 roles, why not pick 2 or more?

So in draft, you pick 2 roles right? why cant riot make it a 2 and more? for instance i usually pick mid/top or mid/jungle, but the n if i go mid/jung i get filled adc where adc is my 4th pick, but the top laner would rather be filled adc than top? you see? So, if riot could let you pick 2 roles, and then optionally ad more roles, then i can pick Mid>Jung>top>Support, and i get filled easyer to the leftmost side? if anyone wana give me their thoughts go ahead.