Because sometimes when you're programming you can rely on your language or framework to abstract away the details of the hardware and operating system. This all

Because sometimes when you're programming you can rely on your language or framework to abstract away the details of the hardware and operating system. This allows you to solve easy problems that language/framework designers have anticipated. Other times, you'll be faced with hard problems that require you to roll up your sleeves and mess with the stuff under the hood. Before you can do this, you need to understand what operating systems do and how they work. If you can write this kind of code, there will be far more problems that you can solve.