The reason we can't always get our main roles
A lot of people here want to be allowed to always get their main role and are willing to wait longer for this to happen. However, I'm only d3 and my queue times are regularly 10-20+ minutes. If everybody could just pick a main role and that only, these queue times would probably over double. Heard the nightmare stories of massive queue times in challenger? Froggen's 4 hour queue time? Imagine if that doubled. Maybe you don't care about massive queue times, but a lot of people do and I'm sure quite a few time lacking people who can't wait half an hour to get into a game will just quit.
I know a lot of you don't give a fuck about the pros and super high elo people, but if this change went through you wouldn't even have to be that high elo to start seeing really long queue times, and the queue times at the top would be absurd.