Article: Writing in 1998 Kurt Jonassohn and Karin Björnson stated that the CPPCG was a legal instrument resulting from a diplomatic compromise. As such the wording of the treaty is not intended to be a definition suitable as a research tool, and although it is used for this purpose, as it has an international legal credibility that others lack, other definitions have also been postulated. Jonassohn and Björnson go on to say that none of these alternative definitions have gained widespread support for various reasons.

Question: The writers Jonassohn and Bjornson cite various reasons for the lack of widespread support of what?
alternative definitions