I highly doubt that France asked Obama not to show up. My guess is that one of three things happened, two directly relating to Obama. Either he is lazy and didn’t want to fly to Europe or he was worried about the political fallout with whatever Muslim groups he’s working with. The alternative is that his staff completely dropped the ball and didn’t comprehend how big of a photo op the unity rally was going to be. To be perfectly honest, I lean towards his staff dropping the ball. By staff I of course mean Valerie Jarrett, though she won’t get blamed by Obama.
It would have been more tactful than asking him not to show up. More likely both sides, neither of which wanted Obama there, would agree that some practicable matter like security not being in place on such short notice made it infeasible for Obama to attend.