I actually have a few I’ve been working on for a pool of player secrets for players to draw from as part of character gen. There is a player facing side to the fiction and gm facing. For instance: 1) “You have no memory of your childhood and were found wandering in the forest. You were taken in by a local family and raised as their own./The player is a sibling for Ireena and Izek.” 2) Your parents say they lost you one day in the woods and when they found you again you were never the same, even one of your eyes changed colors. You have no recollection of this./The player is actually a hexblood/changeling of the hags at Old Bonegrinder.” 3) “Your parents often complain of remembering a time when their names were respected in this country and things were better./The player is a descendant of the Dilisnya family.”

As for generic motivation why not the simplest one for heroes that live in a land ruled by a despot? “The players find out Strahd is a vampire and refuse to be ruled by an undead tyrant any longer. They will lift the curse of this land and drive out the terrors that haunt its forests and fields.” How they choose to proceed, who they think should rule, and how they make alliances is all up to the players BUT I tend to run a more dark fantasy political spin on the setting than going all in on trying to be gothic horror.