It takes Scrooge to scenes from his own past, showing him visions of his own childhood, of his young adulthood and of happier times. The final scene he presents is one that Scrooge cannot bear to witness: his lost love, Belle, with her family.
Perhaps the most clear reason for this is the spirit's parting words of "I told you these were shadows of the things that have been, that they are what they are, do not blame me!"
The Ghost of Christmas Past does nothing but reflect and help Scrooge remember the choices he made, and reflect on them