I think using arch as its basis would clash too much with their target audience. I have not tried Antergos or Manjaro, but at least arch itself is often rather high-maintenance due to its rolling release nature.

I think someone looking for an easy-to-use desktop would not be amused if her/his touchpad stops working one day or the system would not boot properly.

Using a LTS Ubuntu or Debian as a basis allows you to not worry so much about things breaking and focus your energy on the added value you provide.