Third reason is normalcy. I really like normalcy, but all of the Origin characters are rather special. I like special if it's uncommon, not if everyone in the party has a world-altering secret. Have some regular non-secretive people around that just do their job feels more natural to me. Having just a normal human fighter along that fights and shuts up tones it down a bit.
Fourth is focus: I remember Dragon Age or Mass Effect 2, or KotOR, or god forbid both Pathfinder games, where talking to everyone in the camp/castle/ship felt like a chore after a while. I much prefer to be invested in but a few for a playthrough; especially when multiple characters are flirty. But, if I *have* them in the camp, I am compelled to talk to them. It's just how I am. Much better to not have the option. The hireling way ensures the banter and relationships you build have more impact.
