The same reason Reagan spoke a bit of Russian when holding a news conference with Gorbachev - to more directly reach the audience from his counterpart’s home country. The Canadian Press reporter wanted a quote that could go directly to the francophone portion of her audience, and the fact that the US Secretary of State speaks French would certainly be newsworthy in Canada. Interestingly, the reporter’s French article doesn’t mention the refusal, while her English article does.
[quote=DaveBj]it can be difficult to suddenly and on command switch to second language, even when one knows the second language well.
I tend to doubt this was the issue. The question was very open-ended; Kerry could throw out whatever simple phrase or sentence he wanted, maybe “I have great respect for Canada and its hockey prowess.” I think it was more calculated, that he didn’t want the news clips from his first day on the job to show him jabbering in a foreign language.