Docker got popular because a lot of devs gave up on packaging (and declared dependencies and shared libraries) and instead want jails (and isolation and static linking). Now it's self-perpetuating, because it's very easy to put packages into containers but it's hard to package containerized software for use in an ordinary unified namespace (no container).

They gave up on packaging because its a nightmare that never ends. Conflicts, missing dependencies, old versions or no version available for your distro because of course there isn't just one package format.

Docker is still an over-engineered solution to this problem, but its popularity is evidence that there is in fact a problem.

Yep, the question was "package it as what?", and the answer was rarely ever "a statically linked linux executable."

This created the need for piles of configuration management or machine build scripts to deploy the app.

Packaging and jails are simply the means to an end: distribute and run applications.

Docker became popular because it provides an abstraction that simply (and elegantly) eliminates the problem of distributing and running server applications.