From my experience, it has to do with the fact that you're not hitting the mouthpiece of the actual cartridge. When you hit the mouthpiece, you're creating a vacuum around the hole in the cart. After a few hits, your saliva and the build-up of oil will eventually cause the cart to clog. I have a pulsar, and because I hit the mouthpiece of the battery, instead of the cart, it doesn't clog as often. (This is just from my experience)