Before going any further, I'd like to submit a disclaimer. In no way am I suggesting that the "typical RPG adventuring party" of what amounts to a bunch of strangers with no common bonds is 1) BadWrong play or 2) something that happens in every single roleplaying group. But from anecdotal and personal experience it happens often enough and can present certain types of challenges. Hopefully if this has ever been an issue for you, there will be something here you may not have considered before.
A discussion about the community rules in the Burn Shift setting for Fate Core got me thinking about generalizations of player character groups over the years. In particular, the concept of the "murderhobo" - a player character with no ties to anything, who simply moves through the game world wantonly killing and doing whatever they want. Obviously this trope is a gross exaggeration, despite how much the word amuses me. But the reason this stereotype exists is because it does happen to one degree or another, and I would think most gamers have experienced it in one form or the other. It might be the single player who wants to play Stabby Loner McDude who won't cooperate with anyone and wants to bring his swords everywhere; the guy who robs and tortures random NPCs because "it's in character"; or just the entire party having no permanent residence or significant social ties. There are usually other things going on in the group dynamics or with individual players that cause problems, but sometimes it can be chalked up to the characters simply not having a common center.
This setup, especially in it's most chronic form, can lead to a lot of headaches - for the GM and the players. Because having a diverse group of PCs with wildly different backgrounds and motivations, not to mention from far-flung regions in the campaign, can make it difficult create a cohesive group. It can lead to disconnects in expectations and frustrations because the characters only have shallow common goals. There are a number of techniques GMs use to try to get around this, usually by forcing the characters together in some manner (even if it's by saying, "You guys have to be together or this game won't work"). Obviously, many groups work around this in any number of ways. This can result in some very contrived situations as the reclusive netrunner and the socialite fixer have to come up with a reason to work with another, or the paladin and the thief have to constantly dance around the fact the paladin shouldn't tolerate the thief's existence. While either one of those are totally full of role-playing opportunities, the situation should exist with a goal in mind other than, "This is the only way these characters will work together".
Having the players all create characters at the same time, and ensure there's at least some group cohesion is one way around this. The group can also go one step further: have the characters all be a part of a community. This community can be a tribe, family, clan, military unit, criminal cartel, village, town, neighborhood, guild, or whatever works within the setting and the campaign. A social group that the characters care about its success or safety. The idea is that the players all collaborate to build this community and give it characteristics they'd like to see in the game. Once they have a fundamental social hub not only does it help the players feel engaged, but it opens up more opportunities for adventure. It creates situations where the characters have a reason to take action for their community's benefit over their own. Games like Fate Core actually have mechanics for creating the community through the "Fate fractal", either through the use of aspects all the way up to creating the community as a full-fledged character. In other games, it is probably sufficient to record a few things about the community that define it, especially those things that can move the characters to act for the community over their own interests.
There might be unease among some groups about allowing player collaboration to establish setting details, especially something like a faction or social group within the setting. Many settings have groups within their canon material, or it is just tradition to let the GM to decide these things. In those cases, I suggest just keep doing it that way if it works. But at the very least, the GM can try to take the suggestions above into consideration. I'm serious when I say it truly can't hurt.