What I don't understand is why as a society we don't designate those areas non-residential to begin with.
Beneath a flight path should be warehouse / industrial and possibly commercial.
Depends on which areas you're talking about specifically, but many major US airports did start that way. Lots of neighborhoods have grown into the flight paths, not the other way around.
Why don't we keep it that way and protect bigger industrial boundaries around airports? I don't know, but it doesn't seem very realistic; it's too much prime land to control. Commercially zoned areas in every major metropolitan area have been approached, crowded, re-zoned or overtaken by residential development.
Agreed. They should still know better than publishing something with contours out to 35 though! There is already a push by communities to mitigate aviation noise beyond the current level - 55 DNL is a number often thrown around and that often causes debate over ambient noise levels in an urban area etc. This map is going to cause headaches and confusion with the public.