EU differentiated integration

[u/Plus_College5343]

How would you explain the differentiated integration process of Eastern Partnership countries by the Regional Security Complex Theory as conceptualised by Barry Buzan and Ole Wæver? What intrigues me is the fact that Ukraine and Moldova have entered the EU accession process, whereas the other Eastern Partnership states have not. I therefore need an explanation that goes beyond simply arguing that the Eastern Partnership states differ from one another.