It's possible that it was laziness, but i think that another thing you said is more likely the truth: Dajrab was supposed to be the route that isn't the other two. Right from the start it was obvious that some people we meet in the story will not like Tekrok or Rokgrid. Dajrab on the other hand is generally liked or respected by everyone in the story and so joining him could have been the route where everyone we meet would still be close to Sabia too.
A good example is Neve: she avoids Tekrok and so if Sabia is around him, Neve would have to avoid Sabia too.
The problem is the player's experience and development time. For a route like this to work, it would have needed a lot of unique scenes with girls like Neve, Ylva or Vehlis that the other two captains didn't. This would mean way more drawing and so development time, which is sure to be popular now, and people who only play one route would miss out on a lot of scenes with the most popular secondary women, which would cause similarly predictable reactions.
Remember the scene where Sabia and Neve have a threesome with that runaway bandit? Dajrab's route would need about a dozen more of those to work, but i think everybody would rather just have the new patch out already.