So in general there's simply no replacement for the 737 Max. People will be flying on them for the foreseeable future unless something causes a massive drop in air travel.
More expensive than not selling any of them?
Also rushing a new plane is more likely to be a safety risk. The 737 fundamentally is a safe plane - there is plenty knowledge on how to operate it safely. A completely new design would start that from scratch.
Which 737? Have you forgotten the 350 people killed by trying to make the 737 MAX pretend it flies like an earlier model?
But that is exactly the point: a new plane would mean a new learning phase how to operate it safely. It can and should be done, but it isn't a silver bullet, especially none which would arrive withing the next 10 years.
Boeing has spent enough on stock buybacks for three or four clean-sheet 737 redesigns:
https://www.commondreams.org/opinion/boeing-safety-stock-buy...
> Boeing is a world leader in stock buybacks. Between 1998 and 2018, the plane manufacturer also manufactured a whopping $61.0 billion in stock buybacks, amounting to 81.8 percent of its profits.
As the production probably cannot be easily moved, a replacement just isn't available and the market just needs a ton of 737-sized airplanes, the only solution is to up the game along the production line quickly and massively.