Uh, if it'd be to give reasons those were be:
1) The fact that the people don't care about old games like Quake 2 anymore. Yes, Q2 was very popular at its time.. but now it's "unplayed" right now; this adds to coopordie's inactivity a lot, as lnot everyone knows about this mod or want to play it.
Yet, even if Q2 isn't that popular, at least Quake 3 (Quake 3 arena) does a well job on maintaining the Quake serie alive
.
2) The second reason would be the small amount of time the most of the people have got.
Think at something like this:
-let's say there are ~150 constant/active Quake 2 players in total.
-the people have got a specific amount of spare time per day, let's say 1-5 hours; they won't spend all the time on only playing. This reduces their playtime to possibly 10-45-120 minutes.
-the timezones differ, making it harder for people to play together. Also, their spare time might be random, depending on each person's school/working time interval.
--> These things (and more) make it so that the most populated Q2 servers (about 5?) may have only 4-12 players on them.
(10 seconds later)
Edit: and about greeting the new players - that would be nice, though some of the players might not read them / some of them would find it difficult to use the forum's interface to open the messages (
) / some might not even succeed on opening coopordie properly and play etc. Tl;dr: yes.