holy dead guy on a stick! A surveyor in the u.s. would be creaming his or her jeans for that kind of response rate. As you point out, they're critical to the u.s., so it's not exactly like they're doing it out of fear!
Methinks they want a chance to be heard.
I also thought one of the responses was interesting because it mirrored u.ser's tendency to say things like "my doctor is great, but the u.s. healthcare system is awful." Or, "my marriage is wonderful, but marriage as an institution is in decline."
In the u.s., that kind of response has been read as reflective of u.ser's desire to present themselves as successful, happy individuals. IOW, it's read as a consequence of our individualism.
Kelley