Because we have only encountered two clans in the prior two games?
And those happened to fall into the bigoted extremist category.
And who wrote only two clans?
Who chose to portray two clans the same way instead of writing another clan, or portraying them differently to give a more balanced reference?
We could encounter two Dalish clans in DA:O. Instead of creating a third clan in DA2, BioWare chose to bring back one of the two clans we've already seen and make them exactly as friendly as the last one, only less tolerant and less kind.
Dwarves have only two kingdoms remaining, and we've only visited one so far. Instead of making it so the one city we've seen is filled with mostly all unpleasant, xenophobic, standoffish isolationists that the protagonist cannot like, BioWare chose to make the many dwarves within the one city we've seen varied, friendly, etc. If they can make many different dwarves with many different viewpoints and levels of friendliness, tolerance, acceptance of strangers, etc. They can do the same for Dalish.