Because anyone claiming that Boeing is the better choice has to defend their being several years behind schedule in delivering only eight tankers.
The U.S. KC-767 will be U.S. made.
With 100% US components; nothing farmed out to foreign suppliers or contractors?
So now instead of making 108 tankers you are making 8. That is a much smaller program and you still have pretty much the same amount of engineering and testing. So to stay in the black you can't man up the way you would have and the schedule tends to slide.
So do you think that is a good predictor to how Boeing would manage a 179 airplane order?
Also if time is so critical there is an easy way to overcome a 2 year slide or delay (if the contract has to be rebid). Increase the delivery rate. You could easily catch up by building 15 airplanes a year. Both the A-330 and the 767 have been built in much higher numbers and this isn't pushing it at all. That would also give you a chance to replace all 500 in only 38 years.