My guess is that it's because of the supply chain and availability - not so much any superiority of one over the other.
The main difference seems to be that the Carefree model (Carefree Freedom Wall Mount) has poles, whereas the Dometic model (Dometic 9500M) that they decided not to go with does not. Perhaps they decided that having the poles was a positive feature when it came to a manual awning since there wasn't an auto-retract like on the electric that precludes the poles.
Some positives of poles I could imagine:
- less flapping of the awning in winds with or without tie downs
- potentially, could use bug netting below since the weight at the end would be supported
- less stress on the exterior fiberglass walls. Perhaps they can built the trailer lighter using less structural material in the walls since the awning isn't cantilevered
- longer lasting due to less stress on the awning arms