Let me share a little bit more story here.
The original go-raft is one of the first raft implementations. At that time, the raft paper was not even officially published. Many other attempts around that time were not very successful, including go-raft.
Making a production ready consensus algorithm is not easy: https://www.cs.utexas.edu/users/lorenzo/corsi/cs380d/papers/.... Things like pipelining, batching, flow control, asynchronous snapshot were not extensively explored in the context of raft. And not much effort has been put into testing due to the immaturity of the applications of raft at the time.
We realized the problem a few months after etcd alpha was initially released and became popular. However, I went back to CMU to continue my master degree for 1yr, which slowed down the progress.
After I came back from school, together with Blake, Yicheng from CoreOS and later on Ben from Cockroach Labs, we built a solid raft impl as our first priority. Once we put etcd/raft inside etcd2, the stability of etcd greatly improved. That is about 1.5 yr after the initial release. Now etcd/raft powers many production level distributed systems: tikv, cockroachdb, dgraph and many others.
Over the last couples of years, the focus of etcd/raft is always stability and nothing else (although people are blaming us for usability :P).