The house of brands concept is such an efficient strategy because adding new publications does not come with linear growth in costs. While the new publication will need an editor and reporters—or whatever the content team looks like—that doesn’t mean the rest of the company would need to grow linearly.
For example, HR doesn’t need to automatically expand because of the addition of a new publication. Neither does technology, marketing, design, and various other functions at the company. If new publications are continuously added, then yes, more people will be needed. But it’s not 1:1.