I think it was on the air cleaner to make it easier to get to and to design into an existing vehicle to begin with. I've only ever had one fail and it was the original style that had a ballast resistor, not the newer spark or fuel control ones form the 80s. Part of the problem with them is also the sensors that can go bad and throw things out of whack.

In the 90s GM and Ford started putting their ECMs under the hood and most are still doing it with no problems so at the very least Chrysler could have put it on the inner fender and not on the engine itself and that might have saved some potential problems from heat and vibration.