[euromodder]

Drag increased significantly on both, and all similar designs, when the rear clamshell doors were removed.
This resulted in more power and fuel required, less range, more buffeting, lack of pressurisation in transit - i.e. lower transit height, cutting down range even further.
It was also extra work to remove or refit the doors, and that work needed to be done before the actual transport job - the clamshell doors couldn't be opened in flight.

The ultimate result was the disappearance of such designs in favor of the rear loading ramp design on all modern tactical and practical transports C-123, C-130, C141, C-5, C-17, C-27, C-235, C-295, A-400M and all their CCCP counterparts.