Rear chains? Two reasons: Because they are prohibitively expensive, as well as also a PITA to put on—I should explain this: I have another property that I build slash piles on over the spring, summer, and fall. Due to the size of the slash, and the nearness of the slash piles to trees I don't want to damage, I have been waiting for snow before lighting the slash piles off and leaving my tractor over there to manage the fires. After the slash is burned I then drive the tractor back home and then put on chains in the snow and cold, which is a PITA.
The second reason, front chains keep the plow from deflecting and forestry chains (the kind with spikes all the way around) provide plenty of traction without the need for rear tire chains.
What I am going to start doing now, since none of the tires have bead locks, is start airing up the front tires to 45psi, instead of 26 which is what I had been setting them to with the chains on.