I hate spitting. Loathe it. The only things that should come out of a professional footballer's mouth are the answers to my physics homework. Unfortunately, I think it's a bit beyond them.
There is really no reason to spit, Like you said, you never did it whilst exercising, and I manage to go without it as well. Certainly, there are no spitoons in the gym.
Worse still, it is a habit which is appearing amongst people my age, and it's a shame, because it does nothing to help people's opinions of us.