Can anyone explain the reason that the old German accordions had split bellows?

Reinforcement for otherwise too weak bellows? Today's bellows i think, like Galassi, are quite a bit better quality ... - Nout

cheaper for the same strength
they were mostly thin cardboard panels so a long one woulda got all floppy
wle

Simpler to construct if you are lookong for a stronger bellows.

Modern materials make in unnecessary though,MELODIE of Quebec specializes in accordeons with split bellows.

Looks good but doesn't feel or play and different than a modern single bellows.