Trolls in promotion series.

I do not understand how promos work why are you not with other people who are also in promos. I won the first game then got a Teemo top lost that one; followed by a Sej mid and Urgot adc lost that one. Why do they not group promotion series players with people who are also in a series that way people will not troll or pick horribly out of meta picks that are almost guaranteed loses. It would seem only logical to place people in promotion series with other people also in promotion series why is this not done?