The Apple II is widely regarded as the first true personal computer. A computer that anyone could get a hold of and use. But what was it that made this device so popular that it created a new industry?
The first benefit was cost. At $5069, in today's dollars, it was a steal at a time when computers were behemoths costing tens or hundreds of thousands of dollars. But Wozniak was able to achieve that price-point, by simplifying the computer is ways that had never been realized before.
Wozniak never used two parts where one would do. He was not lazy in the design. He figured out how to push everything he could out of the circuits of the time. Sometimes he sacrificed expensive hardware and replaced it with affordable software. Functionally it was more difficult to achieve but it was worth the effort to keep the price down.
Wozniak also made the grand decision to use devices that people already had to interface with the computer. He used the TV as a monitor when it was standard to have a purchase a monitor. This was a simple solutions to an expensive problem.
Admittedly the Apple II was not really interesting to anyone expect hobbyists until spreadsheets were created. But that does not change the fact that the device was still more usable by a wider range of people than many other options. It was one of the first devices that made computers easier and more useful.
The Apple II was so successful because its design was simple and competent. There was nothing wasted. Just everything maximized. But was was the greatest part about it was that it was created by a 26 year old kid that did not have a degree. Wozniak flew in the face of conventional practices and created the first product in an entirely new industry, that others had tried and failed to enter.