Nobody is owed anything, but since publications are the currency of research and the measure by which academics are evaluated, publishing a critique of something as widely and publicly discussed as Piketty's books should be very tempting for academic economists (assuming that economics is a normal academic discipline).

So in front of that background, the silence is suspicious, and the most plausible explanation is that the majority of participants would like to disagree but find themselves unable to put forward such a critique.