Secondary Role Demand

I never get my primary role if I have my secondary as support or fill. Sometimes I have it as support because if I don't get mid, I'd rather play support and let other players carry - or fill because I don't really have a secondary preference. Whenever I do so, I don't get my primary role probably because the secondary is of high demand. I have no problem with playing a couple of games as my secondary role by playing 3 consecutive games without getting my primary is frustrating. I've resorted to picking jungle or bot as my secondary not because I want to play them, but because doing so increases my chances of getting my primary role. There should be a guarantee or at least a factor to allow a player to play their primary every few games even if their secondary is needed to complete a team.