It's always a matter of chasing the bottleneck. It's fair to say that network isn't the bottleneck for most applications. Heuristically, if you're willing to take on the performance impacts of a GC'd language you're probably already not the target audience.

Zero copy is the important part for applications that need to saturate the NIC. For example Netflix integrated encryption into the FreeBSD kernel so they could use sendfile for zero-copy transfers from SSD (in the case of very popular titles) to a TLS stream. Otherwise they would have had two extra copies of every block of video just to encrypt it.

Note however that their actual streaming stack is very different from the application stack. The constraint isn't strictly technical: ISP colocation space is expensive, so they need to have the most juiced machines they can possibly fit in the rack to control costs.

There's an obvious appeal to accomplishing zero-copy by pushing network functionality into user space instead of application functionality into kernel space, so the DPDK evolution is natural.