LP Issue

So statistically speaking you win just as many games as you lose, every single player (not smurfs) has a pretty close win/loss ratio. So why on earth do you get 18lp for winning and you lose 22 for losing?? That's like almost a game and a half set back, like how does that make sense?? How is anyone suppose to climb ranking when going even puts you back from where you started? At the VERY least, it should be an even trade.