Why exactly did they use Ezio in Aѕsaѕsin's Creed II?

Uh, I’m not sure you understand the question, or maybe I just don’t understand your answer, but thanks anyway.

then explain your question further, ive played all the games and the story isn’t that hard to follow really….

They used Ezio because with Ezio, Desmond could get the “bleeding effect” where he took on Ezio’s skills in a matter of days. He did not get any skills from Altair other than Eagle Vision.

I know they needed to train Desmond, and they said something about how they wanted to find the vault, but I didn’t understand.

After the second one I didn’t understand why they still played as desmond but I don’t care.. Fun game. Brohood and Rev not so good tho.

The in-game explanation is that the Assassins needed Desmond to learn more faster and so the operative in the Templar organization arranged for that through cunning and guile.

The out-game explaination is that the sequel needed to be cooler, the storyline needed to progress toward the present day, and it’s all part of the plan more or less.

And change of pace :D