It is cost-cutting that was enabled by technological progress, so all of the above. They've traded repairability for cost, which was a good trade. The time and expertise of the refrigerator repair man are on an inexorable rising trend, just like all other human labor. By making the refrigerator cheap and disposable, they've avoided those costs for the average consumer.
If you want a refrigerator built to last forever, they are on the market. They cost $10k+ and require regular professional maintenance. Restaurants prefer these. You don't need one in your house.
