I'm aware. But it's not "just another purpose". It's a different design. A battery that needs charging is a fundamentally different design choice than a battery that needs replacing. I'd rather a disposable battery that lasts for a year than a rechargeable battery that lasts a week.

> You don't have to remember anything, you just "redock" the stylus when you're done using it and it will charge.

And then you shove your tablet in your bag and the pen falls off. The pen languishes in the bottom of the bag until the next time you want to use it, when it may or may not still be holding a usable charge.

A pen that needs to be stuck to the side of your device regularly is fine for a device that sits on a desk all the time. It's less clearly beneficial for a device that gets handled constantly and goes into and out of bags.