Point of selecting a role?

So I've been playing in the new champ select lately with a couple of friends. I've wanted to play jungle so I always select jungle for primary and maybe mid for my secondary. Ever since then I have never played my primary choice, always the secondary. Nobody else on my team will pick jungle for any role but the one "rando" that we get is the one playing jungle. Is there something I'm missing or do I need to put jungle as my secondary if I want to play it?