Krieghund had this to say in another thread:
SBRs against all ICs were unlimited in Classic (1984), and that didn’t change in Europe (1999) or Pacific (2001). It wasn’t until Revised (2004) was published that any kind of limits on SBR damage were introduced.
I agree that it doesn’t make any sense that an IC with limited production should allow unlimited SBR exposure. Many people, including myself, have played with house rules for many years that limited SBR damage to such ICs.
So, when Pacific was being developed, I’m guessing that little or no thought was given to the impact of SBR damage limits on game balance. Those rules were probably simply inherited from the previous games and taken for granted.
It might be interesting to see what the impact of limiting SBR damage would be. However, I can only assume that it would benefit Japan most, and Japan already has the advantage in the game. You would certainly want to limit only ICs with limited production, as limiting damage to “home” ICs would curtail the US’s ability to reduce Japanese VPs through SBRs.
I’m afraid that’s the best answer that I can give you, since I wasn’t involved in A&A in any official capacity back in those days.