Because they never need? Until Nintendo introduce this feature and people like 'OMG every game company need this for life'.
We never needed analog sticks until they were introduced, as well. Shoulder buttons too. Dual sticks. D-pad. Nobody needs something, until it actually becomes reality, and shows that the old ways no longer suffice.
I don’t care who introduced it. Didn’t Sony do it first, in this analog sticks + motion way? I remember people being very impressed with Vita Uncharted for that.
Fact of the matter is, right analog for quick, fast movement, and motion for fine-tuning is a genuine step up from dual analog alone. Nintendo fans will tell you this. Vita fans will tell you this. Steam Controller fans, both of them, will tell you this.
How could it not be? You get the best of both worlds. The comfortable, traditional two-stick setup, and via gyro, a huge field of motion to land the perfect shots.