There seemed to be an element of not wanting to build another conventional aluminium airplane back then. Recall the blended wing/body studies and artists’ impressions. Remember too the focus on composite construction. The 787 seems to have been an incremental step towards the future as we then understood it: a conventional configuration using new materials, and that was to be followed by an unconventional platform using those same new unconventional materials.
The 787 turned out to be too much too fast, and it sapped Boeing of all of its extra engineering talent and R&D money. That left it unable to do yet another clean sheet design while still being able to afford share buy-backs and other crazy boardroom hijinks. Faced with making money now v. making future money, the future lost. Hence the Max: A ‘66 Chevelle with Apple play.
so why the 737 Max? Greed. And lack of vision. And some hubris. All prosaic human failings that will become the stuff of the next MBa 101 text.