Why is this allowed: Full premade team vs full random team

Second time this happened to me in ranked flex, team full of premade against team of randoms (5 vs 1 1 1 1 1). (I asked my team in both cases if anyone is premade they said no and i went solo as well, identify enemy team was full premade was easy since they all had same club and admited it in chat). http://matchhistory.eune.leagueoflegends.com/en/#match-details/EUN1/1750002995/211753741?tab=overview They get even higher average divisions than mine team. Both games got completely smashed ofc. Should I also mention the troll supp who got probably autofilled and thus banned my intented pick, was ragin in champ select about teemo and picked veigar support because of it. In the end I tried to build locket because he was not building anything to help vayne not to get oneshot by syndra R but it was too late. We even had a one chance when we aced them took baron and attacked nexus but then again the random team showed up when we got split focuses they respawned killed us and defended. Then I shotcalled top, pinged twice im going there, vayne traded death with syndra in enemy jungle and they went 3vs4 rush nexus when I explicitely told them not to and attack t2 top tower. Of course they died immediately and we lost it. So again, why is this allowed?
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