Because they didn't react the way people wanted them to react.
I think when people say this they are over simplifying it on purpose. It's not that they didn't react to things the way people wanted them to but they seem to always be bored, or negative even when there's no cause to be negative.
Giant Cake Show - The show where we talk about the latest in food.
"This little girl is selling icecream cones on the side of the street for $0.50 in the summer? That's worrying, why sell icecream when people should be trying to lose weight, and at that price I wouldn't want to know what's wrong with it, and for all we know it's laced with poison. Yeah something's fishy about this, I don't see why everyone is buying them from her and having parties. I never was a icecream person anyway."
"Eh I went to this restaurant because the latest sandwich was out and ... I'm so tired of food, sure it taste good but why? I don't know."
I haven't watched their stuff in a long time and decided to check them out because of the praise a couple of people gave them on their past E3 conferences saying Giantbomb was a good way to watch them. It was just so very boring and I wished I watched another version instead, like Gametrailers. I stopped caring about their quicklooks when watching them started to annoy me (example, watching them play Shadow of the Colossus, Demon's Souls "People who play this game must be masochists"). Their podcasts long talks about burritos and HAM Radios.
This E3 commentary felt like watching a sports game where the commentator doesn't like the sport or was tired of it. It's better to watch this type of stuff with commentators that are enthusiastic about what they are talking about. It livens the broadcast up rather than drag it down. I like watching some Starcraft 2 commentators that are excited about the stuff that's going on. Not to say people commentating over the conferences should be giving play by play but don't be mopy.
Guy 1 - "So that's what we spent the 4 years making, we'll see you in 30."
Guy 2 - "Come on, date?"
[2016]
Guy 2 - "aw man, really?"
Guy 1 - "I mean, it's a day..."
Multiple people "Yeaahhh"