Actually it is quite active. If you look at d2jsp, you have a new thread for ladder trading every 5min or less.
Spam bots are a pain, but if you're on a full game or a closed game, they can't join.
It gets quite flooded with players at the beggining of the ladder. Message me if you're willing to try it out.
D2/LOD was probably the second online game I played so I'm still have some nostalgia of it, but at this point I just don't see any reason to play it over Path of Exile.