Carr and his people are shrewd. Wouldn't allow Vegas to receive trade compensation, drug out the FA process between NO and NYJ, and also has stated very strongly in a recent interview that he won't be taking a pay cut.
Combine that with Loomis basically giving away any leverage we might have had by pretty much saying Carr's our guy in 2025. Based on these circumstances, if you're Derek Carr, why would you entertain a pay cut?
Loomis is shrewd too. My guess is that Loomis and Carr already had agreed to a deal in principle before the announcement and all they have left is working out some of the exact language of the finer details before the new contract is finalized.
In the film industry, binding deal memos are signed to cover the principle agreement on how much compensation, credits and length of service before a more thorough and detailed contract is hashed out. I'm guessing that NFL teams do something similar. It's basically a written and binding record of a verbal agreement.