Who is going to pay for the creation of those quizzes? Amazon bought Goodreads to minimize its own liabilities, but otherwise it doesn’t want to invest any more money in the site.
Morever, Goodreads doesn’t just cover a few popular fiction or non-fiction works for which a short multiple-choice quiz could be realistically created. It allows you to catalogue and review any book that has an ISBN. As someone involved in an academic field, my Goodreads activity is mainly obscure works of scholarship from university presses.