Primarily because of the success of the CDP in this election, which will bring a lot of the others who left the DP for the HP, mostly because they thought a Koike party would do better than the DP would have, back into the fold. It is a good question should a merger like that go through what will come of the pacts and alliances with the other parties of the left, and at this point, I'm not sure. I would hope and it would make the most since for the CDP to be pretty stringent about their demands and rules for joining.
F**king forum just swallowed my post.
As I was saying - I understand the motivations of those who were all too happy to leave the remnants who now make up the CDP high-and-dry wanting to worm their way into the Next Big Thing, but as I understand from the above Jaichind post, the current coalitions are optimal for energising their bases and limiting opposition splits. With this in mind I don't understand why the CDP would allow them in - even if they were to pledge support for their current policies (ignoring they pledged the opposite to be allowed into Hope).