It&#x27;s mainly cost savings due to the simplicity of 25gbps ethernet vs 40gbps. This article has a good run-down: <a href="http:&#x2F;&#x2F;searchnetworking.techtarget.com&#x2F;feature&#x2F;25-Gigabit-Ethernet-Why-that-why-now-and-whats-next" rel="nofollow">http:&#x2F;&#x2F;searchnetworking.techtarget.com&#x2F;feature&#x2F;25-Gigabit-Et...</a>