I don't understand how you can both appreciate the importance of good design, but at the same time claim that making good design is not a full time job.
It is not true, software needs constant maintenance as the environment keeps changing (which is a sad state of affairs as digital objects don't decay, but pretending this isn't the case is ridiculous).
While you need new designs for new features, you don't need to redesign old features every few years. It's change for the sake of change.