PLaying folks out of position

No reason if I have two 1s who only play center that I can't put one in LF and take the downgrade to a 2...

Sure there is. Some excellent centerfielders--like Ellsbury--don't like playing flies on a curve and often refuse to play the corner spots, even on fill-in occasions. So, since excellent center-fielders wouldn't necessarily just be a "1" downgrade when moved to a corner in MLB, there's no reason to allow them to automatically do so in SOM.