This is an overly negative comment for what is a positive move. Supporting USB-C instead of lightning is good, and it is a reasonable cost to have older accessories face backwards compatibility issues.
The Pencil 2 uses a different technology, with different hardware costs. According to your logic, they should have either not switched to USB-C because a niche accessory has not switched yet, or alternatively, incurred the higher costs and raise price for the consumers (again, for that niche accessory).
Why does it seem so weird that they chose to switch to USB-C while using the adapter as a non-ideal stop-gap solution for that niche use case? It seems like a perfectly reasonable tradeoff.