First, perhaps consider that contributors here are all end-users, just like you.
Other than the site Moderators, Apple neither monitor nor participate within the Apple Support Community forums; as such, if you are looking for a definitive explanation as to why Apple’s Developer Team have implemented specific features in the way that they have, your question will go unanswered by Apple.
Returning to your question, as already outlined, Pencil and finger control gestures are not mirrored. Some touch-gestures are not replicated by equivalent Pencil control - the same is also true of the reverse. As a further twist, if using a Keyboard Touchpad, or separate external Touchpad, some touch-gestures are again different to those of both the iPad screen and the Pencil - very likely as the TouchPads respond to both pressure and multi-touch gestures.
In summary, different input interfaces have different features and control gestures - and not all are mirrored or replicated with alternatives. User Interface design is not necessarily as straightforward as you might intuitively anticipate.
Per my original response, Apple do invite submission of feature requests via its Product Feedback portal:
Product Feedback - Apple
This communication channel would be the most appropriate path to make your comments visible to Apple. While you may not receive an individual reply, we understand that all submissions are both logged and passed to the appropriate team(s).