If you use a site to check games stats (like op.gg) you can see that Games are very one sided. Riot is picking winners before champ select.
I had 3 games last night were the enemy team had 3-4 players on a Winning Streak with Thinks like "Aggressive Laner/Jungler" "Good CSer" "Good Vision"
And my team was full of "Bad with Vayne" "Poor Vision" "Passive Laner/Jungler" "Low Damage Ryze"
When you strat tracking things other then win rate you can very easily see which team will win right from the start.
These 3 games I was top damage in all and lowest deaths and highest kills. Does not matter tho when you have a Junlger that cant jungle and an ADC/Support that are 0/8 combined at 8m in.
Riot REALLY does not like it when you win more then 3 games in a row. It make sure you will loss just as many.