If we don't find ways to price in externalities into the markets and/or the regulations, companies find ways to push things to externalities to cut corners and artificially increase sales and/or profits or have easy ways to market "cheaper" products versus better quality products.
You may want to point fingers at the demand side, but even the most basic, simplified micro-economics is all about how supply-and-demand is a complex dance, supply has more tools up its sleeve than it seems, and a lot more control than demand. Consumers can demand more durable, more reliable products until they are blue in the face, but suppliers are free to just not supply them because cutting corners makes more profits and somewhat happy return customers are more profitable than a very satisfied one-and-done-for-life customer.
Planned obsolescence is a conspiracy theory and there’s no evidence of it occurring at any kind of broad scale.
Consumers generally prefer cheaper, less durable products, which is why the market adapted to better fit that preference.
