1. Because data on an API can reach more places than a traditional website (including a website). With an API your data can flow into weareables, native apps, connected things and even Artificial Intelligence Systems.
Websites, paid banners and SEO techniques belong to the desktop environment. Currently there are more mobile than desktop users and this will only increase dramatically over the next decade.
Mobile users spend only 14% of their time on Mobile Device Browsers, even the best HTML+CSS responsive websites will miss 86% of the mobile user attention and 100% on any Weareable or Connected thing .
The API helps turn your competitors into partners by allowing them to build solutions on top of your data & content. This concept lets partners leverage the existing capabilities of your company and allows you to open new and unexpected revenue streams.