It wasn't so much the fact the you knew the people ..
You knew the guilds by name (raid guilds)
In Vanilla you knew all the 40-man guilds by name and 1/3 officers and even more in TBC we had like 15 raiding guilds (back when 25m was the only way to go) and i can honestly say i knew ALLOT of players back then. Like 5 players per guild by name since you grouped with them occasionaly and talked to them exchanging tactics are all that. It was a 'race' at our own realms pace (it was no top realm) but there really was a good sense of community between the raiding guilds.
In vanilla you had 20 well known guilds and ofc the unknown goofy guilds. But overall the guild were bigger then they are now.
It was different when i played during CATA since there is no progression ladder anymore people don't 'look up' to guilds anymore and thus don't reconise guild tags anymore. Add the 10m guilds as another reason and you get 100's of unknown smaller guilds per realm. It's simply too many to remember.
There are ofc. still the elite well known guilds but it's no quite the same.
The game got allot less depended on larger guilds causing the spawn of many smaller guilds