Because, the Azai clan was tightly keeping the alliance with the Asakura clan as well as building the alliance with the Oda clan, thus the opinion within the family was split over the decision which side to support.
織田氏との同盟関係を構築しながらも以前からの朝倉氏との同盟も堅持していたため、どちらの支援に加わるかで家論が割れたのである。