@SJohnRoss our play wouldn’t be impossible without backstories pre-determined. The problem is that then when given an adventure hook, rather than the player finding a reason why their character would engage, they will sometimes just check out because “their character isn’t really interested in that” but this was never communicated to the DM (because no backstory, duh).
You can either give me hooks you will be interested in, or you have to find a way to be interested in what I give.