It's all about exposure right? You want your website to get as much exposure as possible so that it makes you more money. Whether you're making money through advertising or through online sales, the more people visit your site, the more money you will make.
So how does CDN tie into all of this? CDN makes your site faster. By making your site faster, your site will come up sooner in google searches. It also means that people won't get frustrated or bored while waiting for your site to load. That means they won't just hit that ever tempting back button.