Mobile web continues to be an important platform for a lot of publishers, especially news and media publishers. Mobile is the main channel where people consume media, but publishers still struggle to monetise their traffic. This is true for in-app and even more so for mobile web. On average, news sites receive approximately 40% of their traffic from mobile devices. Also, a comScore comparison shows that the top 1000 mobile web properties have 2.5 times the reach of the top 1000 apps.
Facebook as enabled publishers to use its people-based targeting and ad formats - including native ads - to allow efficient monetization of mobile web traffic.
This is similar to their existing Audience Network product for mobile apps; Facebook is simply extending the delivery of ads to mobile websites. It just takes one click for advertisers to expand their campaigns beyond Facebook and Instagram to reach people across all touch points in the entire mobile ecosystem (app and mobile web).