They recognise that Decentralized exchanges are the way forward and want to be proactive which is obviously good business sense.
Who is to say that in 5 - 10 years, DX may overtake centralized exchanges?
It makes sense to prepare for this eventuality and is prudent to do so. Nobody wants to be left behind.
They spotted Blocknet is the MOST decentralized option that exists right now. (Indeed, it is the ONLY truly decentralized option)
It will be mutually beneficial for both projects. And remember, Blocknet is a protocol. The DX is only the first thing built on that protocol.
This is what they say about it:
Phase 2 of our roadmap focuses on the implementation of the Hybrid Decentralised Exchange Model, designed to accelerate the development of trustless exchanges.
As the field of on-chain exchange matures and new exchange protocols materialise, Ethfinex hopes to act as a zone for experimentation and innovation, accelerating industry-wide learning and facilitating the development of optimal exchange protocols.
Ethfinex will distribute APIs and open-source smart contract tools through which to integrate & interface with other projects and exchange protocols throughout the Ethereum ecosystem. Planned integrations currently include the likes of Melonport, 0x, Blocknet and more.
https://blog.ethfinex.com/the-ethfinex-roadmap-7c7cd82c835c