There's a few aspects to this.
1. as you said, these things are planned obsolescence, done
when a company's business model requires constant new purchases for growth and continued existence. If you make a product that lasts for 50 years without ever needing repair, then you go out of business as soon as everyone has bought one, and there's no need to make very many of the new things.
2. Suppose you go a notch down and you make a product that needs repairs. Human labour, especially in the presence of unions, is extremely expensive, and individual repairs can only be potentially profitable to the repair shops. If it's first party repairs, warranty repairs very quickly eat into whatever original profits you had. My partner once worked at a shop that did air conditioning repairs (like Harry Tuttle in Brazil), They would absolutely refuse to install Samsung air conditioners, since they would always require warranty repairs, and each time you do one of those, you lose money.
3. You get your manufacturing and supply chain so efficient, with economies of scale, and offshoring, you can get the cost of making a new thing way way below the cost of even one repair. One replacement part. The inefficient amount of time spent on diagnostics and maintenance work. Viewed in this light, soldering the ram onto the mother board isn't as much about planned obsolescence as it is about getting the cost of manufacture just a bit cheaper. Your BOM is down now, because you're not paying for the ram connector pieces.
And so, even this is oversimplifying things, but still I believe it's more complicated than evil apple planning obsolescence. And it's more complicated than consumers creating a market that is biased against repairability. It's about the economies of scale enabled by increased industrialisation.
When microchips first came out, computer maintenance people, who were used to working with discrete components, either transistors or vacuum tubes asked "If the circuits are microscopic, how do we repair it?", not quite grasping that repairing a microchip would be a waste of time when you can just replace it with a new one.