They're trying to drive up their volumes in the hope of obtaining more peering. This is evidently the core of Cloudflare's business strategy, emerging in pract

They're trying to drive up their volumes in the hope of obtaining more peering. This is evidently the core of Cloudflare's business strategy, emerging in practically everything they do tactically; from Matthew Prince having an epic public sook earlier this year about AWS's network team telling him to jump in a lake, to this. Peering drives down the marginal cost of bandwidth, and this is super relevant since Cloudflare's main value-add product is DDoS mitigation. Unless you're an incumbent tier 1 carrier (which is the hereditary royalty of networking), the classic ways to obtain more/better peering are either have the most eyeballs, or the most content. A typical access ISP takes the former approach, a CDN like Cloudflare takes the latter. As usual, free anything means you are the commodity being traded on.