Think about it like this: you're not the only person who got placed low. Every single person gets placed lower than their rank. So, if you go into a ranked game right now, you're going to be matched up with other low silver players who got done with their promos and got placed in lower bronze. The actual bronze 4 players will be placed in bronze 5, and will get matched up against each other because their mmr is so low.
Additionally, the mmr reset means that the game is very uncertain about where you belong right now. If you go into games and start winning, the game will rapidly decide that you're better than where it has you ranked and will start matching you up against silver players (and giving you correspondingly increased lp gains).