it's only been tracked since 19XX. if you went to espn or baseball-reference, it's whereever that data ends. (look for any '*' -- like hand-collected data or something included)
it's an option for others, if not for you. simple as that. i would guess that historical play is a little easy to predict and it adds a bit of mystery. you can't out-draft the AI just because you are a baseball history buff traveling back in time
well, you still will if just random splits ratings, but other things you can do too, like allow the development engine to make it all random as far as time/age/TCR effects.