some quick reasons:
Hikers (like myself) pay BIG money to get the lightest gear possible and no real hiker would want to carry a pole that weighs over a pound or so up a mountain. If I need to explain, just carry a 4 pound piece of wood along a ~10 pound backpack up mount Washington and you will definitely understand.
Too many batteries mean that the pole would be front-heavy and really, really unpleasant to lift : you don't lift a hiking pole square, you want the tip to touch the ground ahead of you and it will follow your foot all the way back before you lift it again.
Headlamps are very compact and eliminate the need to bring a pointy hiking pole inside a thin nylon tent at night, or to take your pole along for a bathroom trip.
Your hiking poles go up and down at every step and so the light will go from your feet all the way to skyward.... really annoying!