Not only that but if you did it to enough groups word got around. Blacklist threads were started on the forums for all kinds of offenses and if you were a dick to enough people you couldn't do anything. Even if people just didn't like your attitude or harassment in general chat, that could hinder you. And before server transfers, that meant rerolling in a game that took around 20 days played to hit max level.
There used to be a very strong incentive to not only be nice but help others out and make a good name for your character and make lots of friends on your server. This has slowly declined over the years to the point of non existence. When you got a group together and it went well people usually added each other to their friends list to find again next time they were around. In vanilla wow I had tons of people on my friends list and knew most of the active max level players on my server. There was drama and what not but it was beneficial to be friends with lots of people if you wanted to be successful. Even had friends from the opposite faction, the ones I saw in pvp all the time. There is no incentive to make friends anymore, outside of normal/heroic raids which is a very small subset of the total population. On top of that professions actually had things people wanted to craft with recipes that were difficult to obtain, might only be one or two on a server with an enchant or pattern. Sometimes they were on the opposite faction. There were lists of who could make what on the forums as well. The game was 1000x more social then.
Even if many people only care about themselves, if you make it beneficial to them to help other gamers then they will. If you think that things haven't changed since vanilla/BC days you either didn't play then or were not paying attention.
Convenience for community is the trade off. Yes you get to see all the content but you don't have to make friends to do it now. I really don't mind the easier difficulty levels. I think that is a plus but all these queue systems would be better in a game that had far fewer players. Merge low population realms to allow enough players on a server so that groups are formed easily and you won't need the system anymore. They should also allow people to be in multiple guids to facilitate that social aspect. Maybe not 10 different but at least 3.