I stopped listening for a while after dan left and popped in for random episodes for a long while now but I've noticed it's turned into the Brandon and APL podcast. What happened to people like john coming on?
I'd say it's mostly just been a matter of members losing interest or moving on to do other things with their time.
Sean is right, a lot of people come and go - they lose interest, have a big change in their life, or just simply can't commit the time. It'll probably always happen over time as long as the cast continues to exist.