[briandear]

It's a Contract of Adhesion. Adhesion contracts are, by definition not negotiated.

[fineman]

Not all non-negotiable contacts are a a contract of adhesion. Stores will rarely negotiate (in N.A.), for example.

CoAs require a weaker party, who has no leverage, and it seemingly need to be for a necessity (as part of the "no choice but to agree").

The GPL is an offer, but in no way precludes authors from accepting other terms for use of their work.