I just read a report that originally, Jack in Mass Effect 2 was being written as pansexual, not straight, which makes sense given her threesome reference in dialogue, but they caved under media pressure and made her straight. Seems like such an odd choice to me given FemShep can romance Samara, Morinth, Liara, and sleep with Kelly as well--I wonder why Jack was "too much." In any case, that's the explanation, in case anyone else found this as weird/disappointing as I do.