There were many reasons why players in games like EQ banded together, the most obvious being it took groups to complete meaningful content.
But there were other reasons too.
Nowadays, when I log in to play a game, I have in mind some specific objective I want to pursue. Once I'm in, I go after that objective, either alone or with a group I find on group finder. Usually, by the time I log off, the objective is complete. The mob I wanted was found, killed, and I have the item I need.
It wasn't like that in EQ. Mobs didn't just keep respawning like a Whack-a-Mole arcade game. What you want to fight may not be up, and it could be days or weeks before it is up.
Even if the mob is up, someone else may be fighting it already.
If you did find and kill the mob, it may not drop the item you wanted.
If the item did drop, only ONE item drops, which then had to be rolled for.
The point is, when you logged on in EQ, the chances were very small that you could just schedule your evening to fit your needs and everything would work out by night's end. You couldn't control the game like that.
In that world, people were more apt to check around to see what their friends were doing. They were more open to joining in on whatever was available to do. I used to log on with no preconceived plans at all, and the first thing I would do is check in with guild mates and friends to see what was going on at that moment.
I personally think this is a HUGE difference between older games and new ones, and something that motivated people to more interaction with others.
EQ1, EQ2, SWG, SWTOR, GW, GW2 CoH, CoV, FFXI, WoW, CO, War,TSW and a slew of free trials and beta tests