I think they view this as a job first and foremost, which causes them to do production line-esque shortcuts. Hence the most basic poses and expressions. I find to hard to believe MrDots doesn't know how to make other expressions/poses or hasn't purchased any packages for them. Most of the renders don't use any DOF or interesting framing either. Just straight on with basic lighting.
It's just quicker to do it this way than to do it with more originality/effort. Which is disappointing, because they make plenty of money and can make the games higher quality pretty easily. But they don't, because as mentioned above, it's not "broken". So they don't "fix" it.