When potential customers arrive at your website or look over your marketing materials, they immediately want to know what's in it for them. If that's not obvious, chances are they will move on quickly.
By using the word "you," you begin to establish a connection with readers because you address their needs. And rather than objectifying your message—placing it on a pedestal, as an object of study—you personalize it.
Instead of creating an abstraction, you start to build a relationship.