Why? Fallout had three default characters as option, and so did Fallout 2; why the hell shouldn't FO3 and FO4, and FO5?
*I generally loath so-called RPGs with no backstory for the characters. It's a cop-out, offering "Roleplaying" games with no roles to play. Nothing to sink one's teeth into; RPG gruel.
When there is a complete blank slate character, one plays an infant adult with no past, no acquaintances, and seemingly no means of having survived to their present age... One's character must have fallen out of a hole in the sky, as a cosmic joke.
Developers inherently cannot write to a totally amorphous player character, there have to be at least
some constants in their lives, or you get... Elderscrolls instead of Witcher & Planescape caliber RPGs.
Customization is generally good, but it should be like detailing on the car, not an assembly of user-randomized car parts. RPGS are more about player restriction than freedom; once the player is entirely free to do whatever the hell they want as whomever they want... there is no longer any point to playing ~aside from puerile power fantasy ~and that's not roleplaying, that's player substitution of the PC; it's then no longer "What would/ or could the character do in a situation"; it's "what would the player do in their place?". That's a simulator.
Whether one is playing a Wizard or a Warrior PC in some game, it should be assumed that the character has spent the last several years in intense study and training to perfect (or even grasp) their craft. During that time they would have studied under teachers, possibly with other students; unless they sought out epiphany in a cave. If a PC starts the game at twenty years old, where did they live when they were ten? Consider the three default Fallout characters; they lived their entire lives [up to that point] in an institutionalized environment under conditions akin to that of a Submarine crew at Sea.... and their first step out of the vault is like their first step off of the sub ~having been born in it. That should affect the character's mental state, and their behavior towards others; else they [player or dev] are not accounting for their character's history... and TES [as example] gives no history at all, save the PC being fresh off the boat (or cart, as the case may be). If they spent years on the run or in prison, then someone spent time with them ~even if it was just a guard... They would have a history, possibly friends; certainly enemies, and a few 'frenemies'... and SKILLS. One wouldn't come out as a first level character.
**This BTW is what character classes are for [aside from being drapery for game mechanics]; they reflect the character's previous life choices and the commitments they took prior to the start of the game. It's why they can start out as a competent Soldier/Thief/Ranger/Priest/Diplomat/Merchant, and why they lack affinity for unrelated skill sets. A life long accountant is not going to turn over a new leaf in a week, and become a Ninja for hire... and this is ignored by players lamenting their PC class prevents them from learning swords and martial arts. It's simply contrary to the role.
A blank slate PC is the worst form of lazy design ~
unless the developers support intelligent parsing of a user created biography, and integrate that into the story; nothing does that, and only a few even come close. Arcanum comes close. The flipside is Geralt of Rivia [Witcher 1] ~RPG taken to opposite extreme, and done well. Characters in the world have pre-existing acquaintance or friendship with Geralt, and recognize him; (even if he doesn't recognize
them). This happens in Planescape as well. The middle ground is Baldur's Gate, where the PC has a fixed origin, and established relationships (as with Fallout 1&2, and FO3), but in their case, they are adopted, and a lot of customization remains plausible . The blank slate PC is good for MMOs, but not for RPGs.