Why is ranked still up?

it always like that you got reward but you still can rise your mmr before the soft reset

To expand on what Canadian said, you will keep your current rank throughout pre-season. What this will do is affect your matchmaking in your placements once season 5 starts, so you can get to the same or higher rank if you legitimately play better (and get a few less afk's :P).

As an example. I'm Gold I currently, and let's say I get to plat during pre-season. That means when s5 starts I will be paired with plat-level people while I am still unranked, and if I win a high number of games I could be placed into plat.