Secondary is not cool
Generally, if you've queued up wanting to play one role the champion you had in mind can't be played in another. Very few can do so reliably. But even so, you have to pick a Secondary role. Which along with how it interacts with Autofill creates several problems:
- The champion you actually wanted to play probably can't fill two roles effectively. So you have to pick someone else if you get your secondary. (with a some exceptions)
- Generally, mages who aren't balanced around being at bot don't make good supports-- and can't go anywhere else but mid. For more extreme examples, there are the jungle-only champions like Skarner, Kha'zix, Shyvanna, who can't play at top or mid.
- You don't get Autofill Protection from getting set to your not-actually-preferred Secondary.
- So even after getting Top, which you only picked so you didn't get Support for putting Mid/Fill, which completely changes the pool of champions you can play reliably, you are then still subject to getting Autofilled in the next game. Despite the fact getting your Secondary functions the same.
- Worst yet, Autofill Protection doesn't prevent you from getting your Secondary, or even give you priority for your Primary.
- The reverse of scenario 2, now you've trudged through a game forced to play Support and wanna queue up to finally get Mid. But lo and behold, because you're forced to put a secondary that you're likely to get automatically filled into (since Mid is the most popular role), you end up as Top anyway. And that counts towards losing your Autofill protection.