Ram - a proven design for years.All of that is true.
The simplest answer to OP's question is: They already had a rear suspension design for a light truck sitting around, and it was far, far easier to just copy-paste the 1500 rear onto the Wrangler Front and call it a day than to custom design a new rear end, or custom design an entire suspension package.
The latter would have been the right answer, as the Wrangler front end isn't quite up to serious truck work, and the 1500 rear isn't as good off road. But then the base model would have cost 70K.