Isn't NT-Xent loss commutative?

I think InfoNCE type losses, e.g. NT-Xent from SimCLR v1, are commutative. However, SimCLR v1 mentions in Algorithm 1 that they added the loss after commutating the input of NT-Xent loss: loss = l(a, b) + l(b, a).

Isn’t adding commutated value unnecessary? Thank you ahead.