I have zero reason to perform well on my placement matches. My placement rank when higher, just means a higher loss rate at the end, and I should be optimizing win rate if I want the season chests (because the biggest pip rewards are for wins). Basically you're punished for trying. The harder you try, the worse your win rate because then you'll be matched against people that are better. Also, rank decay isn't that terribad from losses, so it takes forever to lose rank if you're overplaced (as I was last season). A smart person would rather have a higher win rate off the bat (by placing lower on purpose) and then eventually settle on a 50% win rate as opposed to trying harder, losing more than 50% of the time and then finally tanking to a 50% win rate, because getting your rewards is fewer matches played total.
The fix for this is easy. Give a base number of pips per match (like 5) + pips for your rank (1 pip per sub tier after the lowest bronze, so bronze players would get 7 pips per match if they're just shy of silver, the lowest tier doesn't reward any additional pips). The only additional pip that is worth keeping outside of match rewards is the reward for a close match (and it should be upped so people have an incentive to play a long game, 1 pip doesn't feel worth it when you could theoretically wipe and have a chance at another full 10 right now on the next match when you think you're going to lose or in my proposed system a full pip amount). That way you're not being punished for playing your best and rank ACTUALLY MEANS something. Because right now, unless you want to stroke your kitten with your leaderboard rank, your rank is more of a liability than it is an asset