Please don't complain about cost on a pencil they are already selling for $130 they could easily add one and still profit a huge margin, people would even be willing to pay a bit more for it!It's a squeeze to swap to the eraser. A hell of a lot cheaper than having to double up on the sensors in each end. You'd basically need a double-sided pencil just for one function. Would it be cool to twirl the pencil around to erase? Sure. Is it more practical than swapping on the fly? Probably not.
It doesn't change that a squeeze feels very unnatural to anyone used to a pencil and its also easy to toggle it by mistake. Its a worse experience all around just so they can profit a bit more by not having to add extra sensors.