I think that’s because we are not given insight into how the chracters feel. We see the outbursts, etc. but we are not given any hint as to what is actually going on inside their heads, even though we are supposedly in their heads. We are kept at arms-length. It makes the reader feel distanced to the story. Imo.
And the harder part is due to not having an actual story, imo. It’s all about the characters and for this details are more important than for a story-driven book, imo.
Lots of imos. 
