I think there were many options at the time.
Maybe the DCC transfer and easy scriptabilty thanks to Khaled Mardam-Bey's mIRC might be a valid claim.
Perhaps also the impermanence of the history of the channels afforded certain types of interactions that you wouldn't do with you know, theoretically forever scrollbacks.
I guess this brings us back to classical marketing about how you can't have a sustainable differentiated product based on negatives. (as in, this is not the bad guy). You need to have something in the affirmative