something my poll shows is quite consistent (certainly more than 2/3rds of DMs set multiple campaigns in the same setting).
		
		
	 
I've already shown how your poll is skewed.  I show up as running multiple campaigns in the same setting despite running the majority of my campaigns in multiple settings.  
You are guilty of the same mistake that I made - simply creating a binary poll for  behaviour that is anything but binary.  All you've shown is that people are likely to use a given setting more than once.  I'll buy that.  In 10 years of playing 2e, I'd say the vast majority of people reused a setting at least once.
But, my point is, it becomes self fufiliing. You spend the time and/or money developing a setting, you want to get your money's worth and justify the effort.  So, you reuse the setting.  Thus you spend more time in a setting, spending more money and/or effort to expand that setting, thus creating an even larger need to justify the time and expense.
Just to clarify btw, I never said "play once and dump".  That was your interpretation, not mine.  I said that multiyear campaigns in a single setting were a minority.  I also said that I thought that people do move from setting to setting fairly often.  That's a far cry from "play once and dump".  The fact that a third of people thought they'd move to a different setting does show that setting gypsies are hardly a tiny minority.  I am a bit surprised though, I would have thought it was higher.
I've shown (thankfully I think people were able to read past my butchering of the language) that about a third of people intend to jump to a new setting in their next campaign.  Sure, they might come back in the campaign after that, but, that's not my point.
My point is, if you don't spend all that time and/or money on the setting, then there is no need to come back.  If you instead spend all that time/money on adventures and then just hang them together with the barest threads of setting, you can run campaign after campaign, drastically changing setting, without doing any more work.
As I said, you only need about 8 adventures to run a 20 level campaign.  Heck, 8 adventures could easily run a "sweet spot" campaign of 3rd-12th.