I think you will find three key reasons why designers continue to have bizarre parting lines.
1. Not talking to the manufacturing people and truly understanding the mfg process. Particularly in this case an open tool.
2. Industrial Design drives the look of the design and ID likes curves, especially cool blends
3. Designing without ever even trying to "define" a partling line/plane first.
I feel your pain, but don't blame it on the CAD. There are just as many and probably more examples where CAD saves the day in todays lifecycles. If it didn't, we still be on mylar.