"They aren't playing as well as they always do. Not because they have lost motivation, but because their key players are suspended."
Which of the following is implied in the above example:
They have lost motivation, but that has nothing to do with their not playing well.
They haven't lost motivation at all, and the only reason they aren't playing well is the absence of their key players.
If number 1 is correct, that means "not just because" is only a more emphatic version of "not because".
But if number 2 is correct, does that mean "not just because" means the exact opposite (i.e. they have lost motivation, and while that partly accounts for why they aren't playing well, the other and perhaps the main reason is the absence of their key players)?