Luftwaffe crates are also combat buff as well, there isn't really any reason to leave them behind, unless in base.
And for "offensive" OKW crates, 221 drops them one by one, regular 3 stack is "replacement" for med truck tech.
Luftwaffe Supplies and Air Resupply Operation both give combat buffs but they drop 3 of them so one will either use all of them or they will be left in field.
Air Resupply Operation can not be used in base sector.
Regardless being able to move this items in the battlefield would greatly increase their utility if it was possible.
As for OKW only the Opel can move them so it would be an improvement in the utility of the unit.