I don't really know what direction the site will take, but I think you are missing the point there.
The FizzBuzz test might be very easy, but you are assuming that these challenges will be for people of your own skill level. Probably the site will want to cater for a wider audience, from beginner to advanced, and FizzBuzz provides a good starting point for both.
And anyway, we have all read enough about FizzBuzz to know that even "experienced" "professionals" can fail spectacularly at it.
The FizzBuzz test might be very easy, but you are assuming that these challenges will be for people of your own skill level. Probably the site will want to cater for a wider audience, from beginner to advanced, and FizzBuzz provides a good starting point for both.
And anyway, we have all read enough about FizzBuzz to know that even "experienced" "professionals" can fail spectacularly at it.