Nolan chose the blight and the Dust Bowl because they are non-specific environmental crises. The movie is about mankind starting that journey again and exploring space. And these catastrophes provide a reason for leaving earth, are interesting to film, based in history and science, and are not too politically charged (else the movie might just have been viewed as being about a political message, not the Nolans' actual one).
From a 2014 Collider interview by Steve Weintraub with the people behind Interstellar (not just Christopher):
Question: There was an underlying message of environmental pollution and it’s going to raise some discussion, what were you looking at as far as the message you were trying to bring out?
CHRISTOPHER NOLAN: I don’t like to talk about messages so much with films simply because it’s a little more didactic. The reason I’m a filmmaker is to tell stories and so you hope that they will have resonance for people and for the kind of things you’re talking about, but what I always loved about Jonah’s original draft, and we always retained this, was the idea of blight, the idea of there being an agricultural crisis, which has happened historically if you look at the potato famine and so forth. We combined this with ideas taken very much from Ken Burns documentary on the Dust Bowl and spoke to Ken at great length and availed ourselves of his resources, because what struck me about the dust bowl is it was man-made environmental crisis, but one where the imagery – the effect of it was so outlandish we actually had to tone it down for what we put in the film. But the real point is they’re non-specific, that we’re saying that in our story man-kind is being gently nudged off the planet by the earth itself and the reason is non-specific, because we don’t want to be too didactic or too political about it. That’s not really the point. For me it goes back to something Emma said earlier, which was that my excitement about the project was addressing a possibly extremely negative idea, in terms of the planet having had enough of us and suggesting that we go somewhere else, but that being an opportunity, that being a great exciting adventure to be on was something I found very winning about it.
On the idea behind the movie
Jonathan Nolan: So I was rooted in the optimism of what is the next moment in which we start to journey again.
Christopher Nolan: The idea being that with this story you could view the earth as the nest and one day we leave the nest, or the earth is the egg and the egg hatches and we go.