It was a story telling decision. Looking at it by itself, I'm fine with it and thought it was done well. Unfortunately, it comes after the loss of one and possibly two of Hawke's siblings, so it seemed like overkill. Losing Bethany in the Deep Roads bothered me more because I made the decision to bring her along when there was no indication of a problem, other than perhaps being genre savvy. There was no big tell like the conversation in Mass Effect where the person going with the Salarians almost tells you they are going to die... and then you actually have to choose later, making the first choice pointless.
This all ties into what many people had a problem with, even if they didn't realize it or think to put it this way; Hawke is not an active Protagonist. He doesn't affect the things going on around him. He is a reactive character. Things happen TO Hawke. This can be a fine way to do a story, but doesn't work as well in a game where the point is to play and be in control.