The point of there being a primary and secondary is that you will normally get your primary role.
I am an ADC main, and my second best role is support, but I have to queue ADC and Jungle because if I queue ADC and Support, I will get support 9/10 times, which is extremely frustrating.
It's not a problem with the system, it's a problem with the playerbase and the support role. Support is just not a role that people want to play, so they don't queue up for it. The system, needing support players to get games started, pulls them from wherever possible. What Riot needs to do is make the support role something that people want to play, either by incentivizing playing the role, or by completely changing how it works in game.
