In short:

The customer-to-salesperson dynamic is changing.

Instead of talking to your team, your potential customers might be making all of their buying decisions online. And if your written material isn't persuasiveengaging, and thought-out, you might be missing out on some potential purchases. 

That's where a good copywriter comes in. They'll work hard to make sure that those pieces of content that people find online are high quality, interesting, and goal-oriented.