-Demand for cheaper products: Consumers tend to prefer cheaper products. This means cheaper materials and a product that doesn't last as long. Common household appliances cost much less than they did in the earlier half of the 20th century, and people act surprised when they don't last as long as an appliance from the 1950s that cost more than twice as much
-Survivor bias: Only durable products from the past survived, broken and unrepairable products were sent to the landfill. Therefore people only see the most durable products of the past and assume everything made back then was just as durable.
-Technical obsolescence: Old products become less useful as technology progresses. Why use a 100 year old still functional device when it is inefficient and technologically obsolete?
The article even mentions some of these factors with regards to the so-called planned obsolescence of light bulbs. Longer lasting bulbs are dimmer and less efficient, so it makes sense to design them in such a way to maximize light output over a certain timespan.