First, I want to thank everyone for a fantastic discussion thus far!
Let me lay out some math and some hypothetical scenarios:
Let’s posit that Japan will declare war on China and Germany will declare war on France, giving +5 to USA for both actions. USA starts at 6, so this puts us up to 16. Let’s also hypothesize Japan declaring war on the Netherlands on turn 5. It could be sooner, or perhaps a turn later, but for the sake of a general game, let’s assume turn 5. This 2D12 roll is the most important roll of the game and if you leave it purely to luck, it will have an outsized impact on any other roll.
Let’s say USA rolls perfectly average for this 2D12 peacetime income increase for the Japanese invasion of the Money Islands, and gets a 13.

Now, let’s say USA gets just as lucky as Fighting Irish got in Operation Live and Let Die, rolling a 22 upon the invasion of the Money Islands. How would that affect Total USA income?

But even more devastating is the impact of bad luck, like Mad Man Dan got in Operation No Time to Die. Let’s say someone rolls a 4 (the inverse of a 22) for the USA’s peacetime income increase for the hypothetical Japanese invasion of the Dutch East Indies on turn 5:

The difference between good luck and bad luck on just this 2D12 for the Money Islands could be 481-359.5 = 121.5 IPP. That’s just bad or good luck on this one particular 2D12. And note that I didn’t use the worst/best luck. I just used what Fighting Irish rolled as the template. It could have been two better (24) or two worse (2) which would have lead to an even more obscene result.
What I am trying to explain to people is allowing the range of 11 (1-12) on D12’s for peacetime increases is basically saying, “I’m fine with giving or taking away 120 IPP’s to/from USA. Leaving the game to luck is fun for me!” Also, the luck in this single roll affects the turn of entry for USA into the war by 3 turns. Why would people want this? Why would it be fun to have your game so dramatically impacted by the luck of USA peacetime income increases?
Please note that I’m not trying to script the USA peacetime income increases. I’m not saying to change from a D12 to a non-random number. I’m saying we decrease the range of the random number from 11 (1-12) to 5 (1-6). The average result stays the same.
Thanks for reading my long diatribe and I really appreciate the discussion!