Why is the older eren from attack on Titan so cold?

I see quite a few pictures where the older eren is quite cold and unemotional i only looked through the first season of attack on titan and wait until the second season 2 of it comes on netflix. Now to my question what is the reason that they are so cold and emotionless on the pictures

SPOILER:

So Eren switches to the side of the titans and becomes, so to speak, "angry." So I think that's why it is represented.