I don't get the point about DA2. Origins and Mass Effect also only had an excuse main plot that barely - if at all - bound a few side stories together (and they are really similar. REALLY REALLY similar). That's okay of course because not everything needs a strong main plot.
BioWare has always used the basic movie plot structure for all their good games. A movie has to have a centural problem even if that problem is, "I can't relate to my family." BW games always have bigger primary plot points because they make epics (Baldur's Gate 1: stopping Sarevok from starting a war with Amn and ascending to godhood, Baldur's Gate 2: saving Imoen from Irenicus/saving yourself from slayer, Neverwinter Nights: stopping the wailing death from destroying the city then to find all the words of power, KOTOR: find all the pieces of the Star Forge to stop Darth Malak, Mass Effect: stopping the reapers from destroying all sapient life in the galaxy, and Dragon Age Origins: gathering an army to stop the blight from spreading father.
There are side stories, but they connect to a main goal. There is no main goal of Dragon Age 2. I've heard people say that protecting your family is the goal, but if it is then the game is even worse because no matter what you do you'll always end up with just your crazy uncle. Others have said that its a mercenary simulator. I wish. The character gets involved in way too many (in game) political fights for this statement to hold water. DA 2 is three acts that don't have a unifying plot thread to connect them into an over arcing story.
TLDR: Dragon Age 2 didn't have a main plot.