What's the point of ranked placement games?!

"Even if you win all your placement games, you will be placed in a lower spot then when you ended last season." (something like that) So why the hell do they even waste matches for something that DOESN'T matter for placement!? Worst of it you solo ranked and get paired with a bunch of trolls and kids 7 of 10 games and riot thinks they can make this placement games?! what the hell. that's so dumb. For example i started off my placement games 3-0. next games were troll games with intent afk's and the like. now it's 3-3. I ended last season at silver 2, but didn't have time to get gold b4 the season ended. I wouldn't be surprised if they placed me into bronze 5. Esp. with this "auto fill" bs