It's like the girl you don't want to date. You just tell her "it's me not you" rather than tell her what's wrong with her, which would be downright insulting. OTOH, the one you like you can end up courting her for months putting up your best side. Now imagine you're extremely eligible and get a lot of suitors--you tend to develop a knack for diplomacy, and the lesser said the better. Also imagine if you had to sit down with each rejected suitor to explain why they were rejected.

If a corp were to have dialogues with every rejected candidate it would take considerable effort with little to no ROI.