I loved h2h. It helped me to stay in the game as I could not afford or fully understand the MA when I started. It was great for me to learn the basics.
I was actually in the over populated arena when it got banned. Was a great time actually.
The real reason why it was populated more often than now:
Rooms were always open. (Biggest key)
Maps were small and easy (smog 8). Boy do I miss all of the custom maps from AH2.
Having a room that is always open goes a long way, but you need at least 2-4 players in them at all times to spark interest for players to join the arena.
Naming of the arena.
TA57 use to have his room say "Tomcatts FFA furball arena", or Tomcatts Team death Match". Stuff like that.