You just don't buy comics anymore. That's how you quit a medium.
It's not so much a concious effort, it's just something you do. Maybe "quitting" is a bad word, it sounds as if you're going cold turkey on a drug addiction or something. But in reality, it just got to a point where I asked myself "Do I really care how this story is going to end? Do I really care for the fate of these characters?" I realized I didn't, so I stopped buying.
As I said, I figured I'd buy a TPB every now and then if I found a story to my liking, I just haven't found a story I like enough to buy the TPB.
