I think there are many reasons for the "rootless vagabond" trope, and many of them have to do with play style and social contract. First: it is the path of least resistance that casts the widest net. Players don't have to come up with back stories and ties to the campaign, if indeed they have any but the vaguest notions about the campaign and setting. It is enough of a hassle for some casual, beer and pretzels type of players to actually go through the process to build the character mechanically, let alone come up with some connection to the DM's setting. Some people just want kick in doors and smash monsters. In a game that had a strong tradition of players not even naming characters until they survived to a certain level, this can be a par for the course occurrence.
Also, the group dynamic plays a part. If your group is lifelong friends with similar tastes and play styles, with good communication, these things tend to be less of a problem. The DM and the players can set some ground rules about what type of setting and campaign they want to play; if you are a bunch of casual acquaintances that are getting together to "play some D&D" it can be difficult to make expectations and play styles gel, and 'rootless vagabond' can really slot in anywhere.
Also, Also, some people have had conflicts or bad experiences with DMs/games in the past where their idea of what they wanted in the setting and the DM's clashed. Some have felt they were set up to acting out a part in the DM's Magnum Opus unpublished fantasy novel, or become pawns in someone's morality play when they did not wish that type of game. Thus having a connection, like a family or organization/home town was just setting yourself up to have them dangled over a boiling cauldron/raped-and-pillaged while the MacGuffin teetered on the edge of a precipice on the other side of the room/country/continent. Such things can become tiresome after a while too, thus 'Rootless Vagabond' becomes more about just playing the game and getting on with it.
Now I'm not saying any or all of these situations apply to your game, or are valid for your situation, but these are some of the issues I've seen raised in the past by various other players and DMs when something like this has come up.
Also, the group dynamic plays a part. If your group is lifelong friends with similar tastes and play styles, with good communication, these things tend to be less of a problem. The DM and the players can set some ground rules about what type of setting and campaign they want to play; if you are a bunch of casual acquaintances that are getting together to "play some D&D" it can be difficult to make expectations and play styles gel, and 'rootless vagabond' can really slot in anywhere.
Also, Also, some people have had conflicts or bad experiences with DMs/games in the past where their idea of what they wanted in the setting and the DM's clashed. Some have felt they were set up to acting out a part in the DM's Magnum Opus unpublished fantasy novel, or become pawns in someone's morality play when they did not wish that type of game. Thus having a connection, like a family or organization/home town was just setting yourself up to have them dangled over a boiling cauldron/raped-and-pillaged while the MacGuffin teetered on the edge of a precipice on the other side of the room/country/continent. Such things can become tiresome after a while too, thus 'Rootless Vagabond' becomes more about just playing the game and getting on with it.
Now I'm not saying any or all of these situations apply to your game, or are valid for your situation, but these are some of the issues I've seen raised in the past by various other players and DMs when something like this has come up.