Maybe because he has not enough back story. People usually criticizes things and people they don't really know. Also, his face might be seen as lacking personality, be a bit generic. Honestly, I'd add a scar on one of his cheeks to remind the fact that he lost his team and remove some symmetry to his face, and I'd make him take part of some future exotic or catalyst as a mini cutscene that plays in game just like the Bray sisters ones maybe. Or even add a few lines to him in such quests to say something like: "I know you don't like me much but I really need your help for this" or something around those lines, so that you somehow get to have a bit of history with him.