A good PnP adventure is tailored to the preferences of the players and their specific characters. It's impossible to write and run a good RPG adventure without knowing the team.
Just no. Tell your snowflake players to suck it up and shove them down a dungeon. For the half that survives? you may start putting some work on interwining their stories with your stuff, *if* it serves the common enjoyment.
My current, personal view of the game is, you develop your character 90% as you play, 10% when you create the concept. It is OK to start with very little and build up as the adventure advances. It is teamwork. For instance, one of the players may surface some phobia at a time that makes sense for the adventure. Maybe he came up with it on the spot. The DM picks up from there -or not, depending on what's best.
Back in the day, as kids, we slowly tended to the opposite, with two-page backstories and a DM that became the cheap bitch, servicing six different backgrounds full with solo-sessions, personal nemesis, ancestors and whatnot. It was particularly painful when the game fell apart, which happened pretty often given each of the six players felt motivated by very different goals. D'oh!
Now? At least for me, time and opportunities to play are too limited to waste them on all that. Look, I'm not against some of that attention paid to players, but "personal" stuff must be a very small part of what happens in a game table. If having a complex backstory helps the player to RP better, that's fine. Just don't expect the whole world to be related to who killed your parents.
That in regards to backstories. If your problem is mechanics/balance, for instance, "my 5 players want to be an all-thief party, these encounters/challenges are not appropiate!" well, that's extremely easy to adjust and fix, even on the spot.
Finally, it's true that most published modules are shit, but certainly not all are. A game run "as written" of Shadows Over Bogenhafen or Horror on the Orient Express will probably be better than anything 99.9999% of DMs may tailor for their groups.