Because the fact that we increase the sample size is not going to make those who don't want to respond want to respond, and they are not representative of the rest of the population. The fact that we are increasing the sample size just gets probably more middle-income, white, third-generation Canadians into the sample, as opposed to high-income or low-income people, aboriginals, and new immigrants.
On March 8th, 2011. See this statement in context.