Allow me to explain that.
Grouping is an old mechanic that's been in every MMORPG game out there. Get some friends, group up, and do stuff together. But this is old and flawed. Like most RPG foundations it goes back to the mindset from Dungeons & Dragons of old where a fellowship of adventures together delve into a dungeon to beat the monsters, find treasure, and gain experience to improve their abilities. The more people in your fellowship, the easier the challenges.
Nothing wrong with that. Except we're not playing with paper, pencil, and our imaginations here. A video game is a whole other animal. Finding others can be hard to do sometimes if you play at weird times. Even if there is other people around they might not be in a level range for it to be appropriate for the two of you to join together. Plus typically there is the mechanic of grouping causing experience and rewards to be split among the group. If a player can kill the same beast by themselves and reap full reward, why bother splitting the goods with someone else who doesn't significantly help? Especially when the difference between killing by yourself and with even a full group is a time-savings of just a few seconds? Why bother at all?
Even worse is that all MMO's these days are trying to be World of Warcraft were all advancement is based on doing quests. This is nice for a solo experience, but we're playing an online game that we pay a monthly fee to access. If we're playing alone, why not save our money and play an offline RPG that only has a one-time purchase fee? The problem with trying to group while playing quests is that even if a player is around while you are, in the same area you are, and even at the same level of experience you are, if you two are on different quests there is next to no reason at all for you to even consider working together. Especially since in WoW the difference between a solo and a duo kill is about 10 seconds at most. Seriously, there is literally no reason in the world why you would even bother.
So how does ending grouping help with this? Simple, everyone around you is in a group. You help someone, you gain reward even if you aren't "grouped" with them. Heal someone about to die? You get some experience. Jump in when someone is having a tough fight? You get experience. You see someone working on a quest you are? Don't bother trying to set up a group, just jump in and fight. And for the spoils or loot, everyone gets their own. Exploitable, too easy? Who cares? You're helping others, why not reap greater reward even if it was just for a moment?
Why not encourage helping others instead of penalizing it, which is what modern MMO's essentially do. Remove this group mechanic and all the archaic BS that comes with it like splitting reward and experience. Reward player to player interaction, no matter how small or brief it may be. People who would never interact would suddenly find themselves running around together, maybe even striking up a friendship.
The Public Quests of Warhammer Online were something like this. Guild Wars 2 is looking as though they've learned some of these lessons and are applying some of the same ideas into the game. But as it's still in development it remains to be seen how it will play out in practice. I'm looking forward to seeing it.