Placement Result notification

I am currently a platinum 2 player with a 76 lp. Today when I logged into the league client, a notification popped up.

It says placement results league of legends Your Solo/Duo climb begins at SILVER III this season. Please keep in mind that almost all players will start lower than the previous season's rank.

What does this mean? Why do I start at silver 3 when I am at 76 lp platinum 2? I am also on a winning streak so I believed my mmr is pretty high and is around platinum 2 why the hell do i get dropped 2 tiers below my current level/mmr?