When you begin a new campaign, do you prefer the PCs to be visitors in their very first settlement, or do you prefer them to have been born and raised there? Are they the wandering heroes who stumbled upon a city and witness its troubles, or are they longtime citizens who finally decide to make a name for themselves in this city/village/kingdom?
In most of my games, that's really up to the player and not me. It is highly useful if one or more members of the party have a natural connection to each other, and so I encourage players to weave their backgrounds together somewhat, but basically any background that fits the setting and ensures the PC has a motive to participate is going to get approved. Generally, when I try to put a constraint on a background, I try to keep it very minimal. For example, I might set a constraint where every player has to explain how they know and are on friendly relations with a particular NPC, but this would never constrain things as tightly as you do here. Occasionally I have run themed campaigns where everyone has to be an elf, or everyone has to be an evil demihuman, but even then you probably could wiggle out of tight constraints on where you were from.
For my ongoing campaign, the following briefly explains the situation of the PC's at beginning of the game:
PC #1: Officially a laybrother in the temple of the goddess of arts and beauty, the PC was actually a member of a heretical order of assassins within that temple tracking down a notorious necromancer.
PC #2: A cleric sent to encourage the worship of the goddess of the sun and tend the neglected shrine of that goddess. He was originally from a distant region where sun goddess worship was more prevalent, but was casually acquainted with PC #1 from their time in school together in a different city.
PC #3: A laybrother of the temple of the god of death and travelers who had been pledged to the temple as a three year old child. He was just returning to the city after two years spent guarding pilgrims on their journeys.
PC #4: A prostitute and member of the inner circle of the Guild of the Painted Lady, the thieves guild that ruled criminal interests in this region.
PC #5: A sailor and sometime pirate who had recently escaped marooning. He was friend and customer of PC #4, as well as a close childhood friend of PC #2.
PC #6: A brutish sailor from a distant barbaric region. He was at the start of the campaign just arriving in the city on shore leave.
So of the six, only three were natives of the city, and only one wasn't newly come to the city since two of the natives had been absent elsewhere for years. The party split somewhat into two groups by interests and motivation, but PC's #2 and #5 bridged the two groups, and they were united initially by the need to just survive.
This would also be a good example of why metagaming isn't always bad. While there was enough going on here to give a color of why this group formed, ultimately there is no reason that this group would have to be together beyond the fact that they are all PC's. Yet, if a player in the group acted as if he didn't realize the other PC's were PC's and so special - something that the player knows that the PC could not possibly know - this would have been bad roleplaying. Instead, the proper thing to do is assume temporarily Author Stance based on the knowledge that if the cooperative game is to continue, the party must form a fast and lasting alliance. To assume Actor Stance here to the extent that you decided your character just wouldn't continue with this group because it wasn't in character, instead of finding some color of character that excused the choice would not be IMO mature RPing. That said, it's up to everyone to cooperate with that and not immediately try to offend the morals and ethics of the rest of the PCs, but instead maturely find some color that lets you both express the character in a way that is true to the character, but which also lets the game continue.
The relationship between Roy and Belkar Bitterleaf in OotS is exemplary in this regard, and should be used as a model for both staying true to a character and yet finding a way to keep the group together.
That may seem a bit of a tangent, but it is I find very central to any discussion of what makes a good background or character.