Ranked Placement System

So how come the placements are ridiculously lenient your first season and trash every season after? I went 8 and 2 in placements, positive scores in every game, and was placed Bronze 5 since i didnt play ranked the season before. My friend a new lvl 30 for like a few weeks, went 4 and 6 with some sub par games and got silver 5. Season 3 when i first did ranked i started silver 5 but decayed out because i was away for military training. Why is the system like 90% based off your prev season rather than your placement wins and scores. And dont give me that mmr bullshit because god forbid you play with a friend in this game.