Because the question is who is the GOAT. I don't know isn't a very thoughtful answer.
I started the thread by comparing both of their accomplishments.
I find that they are equal in Championships but Brady surpasses Montana in overall playoff success.
I find that Brady surpasses Montana in regular season success. And its not very close.
I find that Brady statistically was better. This is the least important to me, and the differences in era, which are very small by the way, mean little.
What argument is their for Montana?
I think its fair to say the Brady was at least as criticial to his team as Montana was, and probably more. Montana typically had a better running game and better defense.
I put heavy emphasis on ACCOMPLISHMENTS because that is why you play the game. Strip everything else away, and who wins is what matters regardless of how you got there. The difference being that QBs today are by far the primary reason their teams succeed or fail, while in the early 80s and before that was not the case.
Feel free to give reasons that you think Montana should be considered equal to Brady beyond the 4 rings, but I just don't see any, and "I don't know" isn't a valid answer to me.