Shouldn't Apple consider allowing use of Apple Pencil while it's charging?
Apparently Apple disables drawing functionality while Apple Pencil is charging for performance reasons. So, the behavior is by design.


Cannot use Apple Pencil while charging



  No, we disable the drawing functionality while it is charging (performance reasons). Although you can charge with a Lightning cable, it will charge much faster when connected directly to the iPad Pro.


In case you find a product feature concerning, you can always share feedback with Apple using the Product Feedback webpage:


Product Feedback - Apple