If you really want to single that out of my entire post, then lets have at 'er. Canon technically doesn't need to do anything. In fact, Canon doesn't even need to make a 7Dmk II if they don't want to. Perhaps I and many others are just hoping that it's a "game changer."
People are buying the current 7D. If the MKII has no real innovations - 20MP, 70D LiveView AF, slightly improved AF, 10 fps - it will still sell just as well as the MkI, but for a higher price.
Of course it will sell and the term "game changer" is open to interpretation. It's subjective. What I think is game changing, another may not.
However, there is a reason why I never upgraded to the T3i when it came out. Or the T4i or the T5i. But you can bet your bottom dollar that this duel pixel CMOS AF technology caught my attention (and can arguably be defined as game changing by people who are also into the video side of things), which brings us back to your original question of why?
Canon is a business and most businesses # 1 goal is profit maximization. In order to maximize profit, Canon needs to convince as many people as they possibly can that the 7d mk II is worth buying. Not just beginners, but also for people like myself, who are looking to upgrade.