Everything is designed to last between a few years and a decade, with the expectation that there's no point engineering for longer than that because something better will replace it by then. This feels bad but it's generally correct. Practically every aspect of technology is improving so fast there's little point trying to engineer things that last, because a stronger, cheaper, lighter, thinner thing will be available long before the thing has expired.
Planned obsolescence isn't only a thing with fast moving technology either. Engineers design bridges with a finite lifespan in mind as well, and it's not because they think there'll be a much better bridge in X years. It's just that the relationship between the expected lifespan of a thing and its cost to develop is exponential.
Agile is a response to this, not the cause.