> Why would Airbus spend 10 Billion on RD for a new plane if they can only spend 1.5 Billion on RD to modify an existing design?
Because that's what manufacturers always did? If you only do iterative changes then eventually you run into a wall. Boeing engineers also knew that. The disagreement between what engineers wanted and what management wanted has been a point of contention for many years.
See, that wall is not a problem when you are in a duopoly. You will need to jump the wall only if your competitor jumps and why your competitor would jump if you can pocket the 8.5 billions and sell the regular stuff?
That was what Boeing and Airbus supposed to do: Sell the a320Neo and 737MAX for as long as possible and stay away from the wall. Now that Boeing screwed up, they may be forced to jump the wall and Airbus will have to follow. On the other side of the wall, they will sell the same number of planes.
Full-scale redesigns require more than a ton of capital to build the new plane. It will cost your customers a ton of capital to buy the new plane and change their entire setup (pilots, mx) to use the new plane. The airlines want new jets even less than the manufacturers want to pay to design them.
Because that's what manufacturers always did? If you only do iterative changes then eventually you run into a wall. Boeing engineers also knew that. The disagreement between what engineers wanted and what management wanted has been a point of contention for many years.