Jimmy dugan is talking about the prevalence of it for the fact that they use it in the game
Step-by-step explanation:
Chewing tobacco was used by lots of ball players, as in baseball and it is used primarily for stimulation as most players learn it through the culture of playing the game to chew tobacco.
Chewing keeps saliva in the mouth with which they can moisten their gloves and the ball. It also helps keeping the mouth wet and keeping the person focused on the game as any with the habit would say.
This is why many players used to use Tobacco and even Jimmy does as he would later succumb to it.