I think it's not exactly true that he can't feel something. There are some lines in the game that make us realize that he may still have emotions.
First of all, some old lore books tell us that Mindflayers have emotions. In most cases they are negative emotions, but this is not always the case. There are exceptions, not many, but they do exist.
Some of the lines in the game suggest that the Emperor has some sort of feelings, and there's even a scene where you can feel his emotions yourself. I mean, it would be possible to develop something deeper from that, the lines are there, the choices are there, the only problem is, the consequences of these choices are not... And we are talking about a game where your choices matter.
