# Why is SKEYSEED derived using the nonce as a key?

In IKEv2, SKEYSEED, which is used to as a seed for generating the rest of the keys, is generated as

SKEYSEED = prf(Ni | Nr, g^ir)

In other words, we invoke a pseudorandom function with the concatenation of the initiator and receiver nonces (that are sent in the clear) as the secret, and the Diffie-Hellman shared secret g^ir as the seed.

What is the rationale for this? Shouldn't the arguments for prf be reversed so that the secret is actually, well, secret?