Because the human population grows, so concepts such as societies and economies follow. It's that simple. You can run a small business that remains at a steady state but you still need constant customers to remain viable, and even if every company stayed small there would be new ones started, so growth is inherent.
Marketing spend is a proportion of GDP so it'll scale along with it, and is thus not zero-sum. As for regulation, that is needed in the industry and why we have limits on certain categories.
