I think docker itself had plenty of time to innovate. They could have solved the problem long before mainstream got a hold of kubernetes. They just didn't solve the actual problems users where having at that time, which was container orchestration across multiple servers. They went very very deep with a lot of drivers and API changes and what not. If I am not mistaken docker-compose wasn't even a part of docker first before it got bundled, someone else was solving docker's same-server orchestration problems.

Kubernetes is for a lot of organisations pretty difficult and way too much for a start. We used rancher for solving our problems which did a fine job, rancher got a worse when they made the move to Kubernetes.

In the beginning they (docker) also removed a lot of options like cpu throttling and configuration and such that LXC had from the start. They also had their own version (a shim) of pid 1, some point at the time. And other things that made it a little painful to properly containerise. I was often very frustrated by docker and fell back on lxc.

There was also something with the management of docker images like pruning and cleaning and other of much needed functionality that just didn't get included.

Also something with the container registries which I a this point can't remember (maybe deleting images or authentication out of the box or something that made it hard to host yourself).

Anyway I think it's failed because it failed to listen to its users and act upon them. They really had a lot of chances I think. I think they just made some wrong business decisions. I always felt they had a strong technical CTO that really was deep on the product but not on the whole pipeline from dev->x->prod workflows.