The numbers just don't add up.
In this scene, what does "The numbers just don't add up." mean?
A: There's only so much love to go around.
B: We could share.
A: The numbers just don't add up. There's not enough love for the two of us.
I know 'add up' means 'make sense', but I don't know why he said THE NUMBERS don't add up, not IT doesn't add up. Why?
Thank you!