Snow chains - why only on the front?

Manual suggests to mount chains only on the front, not the rear axle. This recommendation does not vary across fwd and awd vehicles. On my landcruiser 100 i used chains on all 4 wheels. Anyone knows why only front is recommended for the bZ ? 

For better steering and control of the vehicle.

As mentioned I have tried 4-wheel chained up landcruiser. It had diff-locks all around. Why would you say control would improve with chains up front without also in the rear on the awd bZ?

I suspect the manual was written with only the FWD version in mind, but even on the AWD the front wheels are the main driving wheels, and you don't want the rear wheels having more driving traction than the front or you'll have the same problem RWD cars do in the snow and ice.

SAAB, who should know, recommended all wheels.  The car was FWD but each brake circuit operated on 3 wheels.