More than just lack of competition, cost-cutting measures or planned obsolescence - I think this also has to do with what marketing. Consumers will buy devices

More than just lack of competition, cost-cutting measures or planned obsolescence - I think this also has to do with what marketing. Consumers will buy devices that feel attractive. Shiny touch screens sell. Shiny plastic sells. Over-the-top features sell. Boring mechanical machines don't sell. Thick and sturdy looking metal doesn't sell. Customers want the advanced features which make these once-simple devices complicated and more error-prone and they also want their devices to be more lightweight (hence more plastic and thinner metal) and be curvy, not boxlike (which is why we stopped having smooth surfaces).