Because it adds complexity to the user experience. Most people don't need handwritten notes. How would a stylus help with their text messaging or photo taking? They're fine just pressing on the on-screen keyboard. Hell, they don't even teach cursive writing in school anymore. So, a stylus is STILL not a valid useful device for the average person.

You'll notice that they introduced this stylus for the iPad Pro, and not for the regular iPad. This stylus is for a specific pro user that actually needs a pen input.