JG is largely unproven, if very promising.
Rodgers was probably the best player at his position when he signed the current deal. The comparison between players doesn't make sense. Its what the going rate is for good starting QBs that you are looking for.
If JG got $37 mil in the first year, Rodgers 38.5, and he will get more this time.
But Rodgers has not asked for a renegotiation at all during the contract. So your point about it never being enough likely doesn't come into play. The only way its not enough is if Rodgers (and maybe the Packers) decide its time to move on.