I was tempted to add to An adjective to describe a pregnant woman's swollen belly?, but there's no answer button, and the explanation is a minimum rep of 10, and I've got (thanks to association) 101. ?
Because the association bonus doesn't count towards answering protected questions. The bonus is granted to give you some basic privileges because you've proven you understand how the Stack Exchange software works in general. The purpose of protecting a question is to prevent poor answers from users who haven't proven they know how to make quality contributions to a site. The former does not imply the latter; just because you have a bunch of rep on Stackoverflow (and thus know how to code) doesn't mean you're knowledgeable about English, gardening, bicycles, travel, etc.