Baseball has always been a sport based mainly upon tradition. People fear change, and Major League Baseball is no different.
Nearly everything you see on this list comes from the past 35 years or so. Prior to that time, there was little room for individuality in the game. It was about tradition and the team. Players weren't supposed to bring any added attention to themselves except from their play on the field.
These accessories come in several different categories including equipment, style and habits. Players have been allowed to express their personalities and their individuality during this recent 35 year time frame.
I may have missed something, so if that's the case please share.