Ranked game remake lowers mmr

So I found out that even though I wasn't the leaver in a ranked game I still lost 150 mmr from 1 remake. How is this possible? I was matching with plat 4s and 3s and was at 1789 or so mmr and from 1 remake it brought me down to 1600 or so mmr.

Now I understand that riot keeps true mmr a secret but I can tell that I immediately got matched with gold 3 and gold 4s just from that 1 remake and they all had normal gold 3 gold 4 mmr. So my question is why does riot do this even though I wasn't the one leaving I still got penalized?