Don’t developers always know what the content of a site will be ahead of time? In other words, don’t developers create sites around content?
No. While it is best to design around content, this isn’t always possible. For example, say you are creating a Wordpress theme for a client. Content Management Systems like Wordpress allow users to easily add, remove, and change the content a site. You can imagine a scenario where your client swaps out content or adds new content to the theme you created.
In this type of a scenario, the developer might not know what content the client might use to populate their theme.