Baseball is a long, slow game where one engages in long stretches of absolutely nothing punctuated by a few brief moments that require instant and total concentration. For professional ballplayers, it also includes a very long season full of travel, which, of course, is not conducive to developing an adequate sleep schedule. Nicotine is a fast acting, legal stimulant that enhances concentration and energy levels with minimal initial side effects (unlike caffiene, for instance, which makes you jittery). Smoking is both difficult to manage while playing baseball and it negatively impacts athletic performance. Smokeless tobacco is an easy-to-manage delivery system for a stimulant which baseball hasn't banned.

Duh.