most strawhats are pretty mystery. not saying their own history might be intersting, but we know next to nothing about their family and stuff.
Zoro: young boy mysteriously shows up at dojo and trains there for 10 years. doesn't he have any friends/family or anythign wondering where he is. where did he grow up, ect.
Sanji: he was a 8 year old chef on a ship. again where was his parents ect, how he get to that ship.
nami: did her parents die in that attack? who where they
Franky: who was the pirate crew, who are his parents.
Brook: what inspired him to be pirate, his parents, how he got into music
robin: who is her dad
Chopper: hmm nothing really more for him
Usopp: hmm again nothing really more to discuss
But one thing we should not rely on is, those pasts/history could be boring as heck and not mean or do anything. Not everyone has to have some magical connection to something or someone and have some insane family or hidden past.
so sure we could get some more on their past, but again it could be not even worth reading about.