Old ones did a few things really well; they typically have the hot radiator coils on top, or better separated from the internals (at the cost of space) better insulation (at the cost of internal space), and didnt have built in defrosters (or air circulation). They also used a somewhat more effective (but worse for the environment) refrigerant, freon.

After the 50s, we demanded a larger volume, not just being larger but also sacrificing insulation and ideal hot-side placement. And we had to change the refrigerant used (and get rid of latching doors). Several features that were poor from an energy standpoint became standard (auto-defrost, air circulation).