If senator's phone lines were crammed-full of citizens demanding knowledge of the negotiations, then the citizens would get that knowledge. But they don't. No one cares or even knows about this.
When the executive negotiates without Congress's participation, citizens don't get a say in the process. We don't get to review the agreement, or pressure our representatives into changing or rejecting it. However, special industry groups do, including the RIAA, as advisors to USTR.