The thing about mass manufacturing is they're only gonna do things that improve their bottom line (or at least that they expect to), because ultimately the car buyer is not the customer, the shareholder is. If it's more expensive to do, then they have identified a reason to expect a return on investment.
A change that increases part cost that is not going to be noticed by the typical buyer won't bring additional sales so it would be expected to provide a return in reduced warranty claims, assembly labor, supply chain efficiencies, or a combination of those.
On the JK axle tubes they apparently decided that a beefier axle would not bring the additional sales or reduced warranty cost to justify the cost of the parts to upgrade all of the models, or to split the volume into multiple parts which would increase the per-unit cost of the original part as well. Unfortunately for the offroad enthusiast, they were probably right. We're not their target market as much as we'd like to be.
