Riot please explain this Matchmaking Logic.

I'm Silver 2. I got matched into a game, and everyone on my team we had S2, S2, S3, S3, and an Unranked. on The enemy team, They had G5, S1, S2, S2, S2.

Now, I'm not complaining that we had an unranked adc. He was probably in his placements and that's understandable. But WHY was my Unranked ADC matched against a Gold 5 Enemy ADC? Their ADC ended up going 17/0/2 and we stood no chance. I'm not blaming my poor adc because he was just trying to do his placements. Why was he matched against a Gold ADC main in a Silver 3 MMR game? It isn't fair for him, and it isn't fair for the rest of our team.