That's the kicker that got them over the line. Look at usage graphs and docker is running circles around Linux containers. I use docker professionally but privately will use lxd barring some complicated setups that are a docker pull away.
Truly can't stand some of their design choices, eg the utter distain for iptables and even non-technical ones like requiring signup to get the daemon on Windows/Mac, it's frustrating software overall whose only saving grace is the ecosystem around it.
People assume that just because Docker and lxd do "containers", they are somehow equivalent and it's simply a matter of choosing between the two. But they are far from equivalent. It's not a choice between two competing technologies that achieve the same goal at all.
Personally I will prefer model like Guix System instead of container to run systems and services.I find that solution to be much more elegant than Linux containers or distributions. Linux containers initially came as chroot, jails and zones and than addition of cgroups and namespaces by google made it popular as lxc and later adopted and forked by Docker to make something complicated. These are bolt on solution to have immutable infrastructure. Guix is designed from ground up to be new OS for 21st century server and application infrastructure. May be it will or one of its derivative will become mainstream in time to come.
Don’t get me wrong, Docker has made some stupid technology decisions, but the network effect of so many adopters means that it should be the default choice for any container situation.