In my manufacturing experience "designed obsolescence" is definitely a real phenomenon. I don't attribute it to malice on the part of the manufacturers. It is the result of competing design criteria which results in items that don't last as long as comparable products of generations past.
Consumers don't generally prefer to pay more if they believe they can get a comparable product at less expense. Most consumers are not capable of determining the engineering sufficiency or manufacturing quality of the products they buy. So if two items look pretty similar and make similar claims of performance and longevity, the consumer typically opts for the lower cost item.
To reduce product price and stay competitive one of the simplest techniques is to reduce component weights. The global supply chains for manufacturers of complex machinery like cars or tractors are mind boggling. Individual components get shipped from place to place across oceans and continents as raw materials become parts and parts become sub-assemblies and on and on until a final product is readied and shipped to a dealer's lot.
Another good technique to reduce cost is to change the material used to construct a part to a less expensive material. This often results in using a material less suited to the task, but it is an engineers job to try and make a component that is still suited to purpose, but less costly.
Overall, consumer price pressures and government efficiency edicts have guided manufacturers' engineering choices to produce items which are more lightly built and have shorter overall life expectancies. Are we all better off? Sometimes we are, sometimes maybe not.
