Picking your Roles

When in a draft lobby, one must pick the roles they want to play, but for some reason Riot starts limiting you on what you can play once you hit 2-4 players. I dont understand why they do this, if I'd like to play certain roles I choose them, and if in turn, that gives me a 5min queue timer, then so be it. At least I was able to grab the role I specifically wanted, not that Riot forced me to because they think my team isn't divorce enough. Just wanted to put my thought out there, as this has been frustrating me and my friends recently.