Because non of us have time to create content that doesn't get us closer to our goal.
Note: It's not traffic. It's better to have a low-traffic site that achieves your goal than one with way more traffic that doesn't. Not all traffic is created equal and not everybody that visits your site is ultimately going to reach that goal you have for them.
Depending on what kind of site you are running, maybe your goal is to get:
All these kinds of things can be boiled down to one thing, and that is revenue or stored potential for revenue.
Each piece of content also has its own goal, which contributes to the big picture.
It's easier if you pick a niche.
