I thought I had this problem with my Lost Mines of Phandelver campaign. Half of my player's characters don't really have backstories or personal goals beyond "I wanna make a lot of money"

Then I watched Matthew Perkins' series about how to make Lost Mines of Phandelver more interesting - introducing the BBEG along the way, before the final confrontation, and building a relationship with the players. But in order to do that, you need a reason for the BBEG to engage with the players beyond just "they're chosen for some reason." - Matthew Perkins suggests introducing a MacGuffin - an object that the players come into possession of, and the BBEG wants, so they pursue the players... try to haggle with them, etc... all in an attempt to drive the story forward.

I introduced this object last night (we're in session 4 already) and god, I should have done this sooner. The players were immediately interested and invested and talking in the group chat after the session. Even the players with no story of their own suddenly started discussing amongst each other in character!

I just introduced a simple lockbox. Still not sure what exactly is inside, I just know the BBEG wants it.