Mostly because of vertical integration, and Apple being more vertically integrated in comparison to other PC manufacturers. Simply put, when you design and bui

Mostly because of vertical integration, and Apple being more vertically integrated in comparison to other PC manufacturers. Simply put, when you design and build every single thing that goes into a complex product, you then have complete control over everything that makes up that product, and thus have complete control over that resulting product's quality. A more vertically integrated company is thus in a better position to make a better quality product - particularly so, because it has a better potential to address any quality issues stemming from where separate components interface. Think about it, if you build an assembled product using parts sourced from third parties (ie you're not vertically integrated), you are somewhat at the mercy of third parties and the quality of their parts. On one end, this can be beneficial (or bad), as you can reap quality gains anytime you're vendors improve the quality of their parts (and vice versa). But, generally speaking, vendors are only interested in the quality of their part/product, not necessarily your downstream product which sources their part/product as a component. As so, new quality problems can arise from integrating separate parts, of which your vendors may not care much to address, but you at times can't address them either (in the best possible way) because it would take slight changes to each of the vendor's products, at which you're at the mercy of your vendors to change but it's not really in their interest to do so. As so, from a holistic viewpoint (your assembled product), you can end up being stuck with a suboptimal solution (ie lower quality product).