One sticking point which rattles the ROC is the fact that this Council reviewed procedures by which an Orthodox Church could obtain autocephaly.
Given the issues in Ukraine and the conflict with the Kyivan Patriarchate, as well as the MP's refusal to grant autocephaly to the UOC-MP etc., it sort of made ecclesial-political sense for the MP to stay away.
However, the absence of the MP, the Georgian and Bulgarian Churches only served to underline the charges of Orthodox detractors re: lack of a central authority figure like the Pope. In any event, the MP sees itself as having greater ecclesial power and therefore leadership potential than the EP. But any change in that regard would require an Ecumenical Council to establish which would be difficult if the MP refused to attend it.
As an EC, I greatly admire His All-Holiness the Ecumenical Patriarch and see him as the first among equals in the Christian East. He is my patriarch too!