Everything I know about pilgrim hats tells me that buckles were in wide use by the 17th century. So what happened to your belt buckles, Lou Gehrig, Jimmie Foxx, and Babe Ruth?
Note also the odd placement of belt loops on the Yankees' trousers.
My best guess is they moved the buckles to the side so as not to interfere with ... head first slides? My second-best guess is that wearing your buckle to the side was the style at the time, like tying an onion to your belt during the Roaring Dickities*.
* Stupid Kaiser.