The story is rather simple.
1) Prices went up a lot
2) Nobody could afford to buy anymore
3) People still wanted to sell so active listings rose significantly
4) People still can't afford to buy and sales dropped off a cliff.
5) Consequently the months of inventory rose to unprecendented levels.
6) Prices began to moderate.
7) Prices began to fall
8) Prices began to fall quickly.
9) Prices are now lower than one year ago.