Not a founder. The catch is that docker fixes the Linux dependency hell problem that stems from the fact that the server Linux distribution may not have the dependencies you need for running your application and if you install your dependencies that are not in the distro repository, such as shared libraries or other executables, that may override the existing ones and mess the system or break something. Even a native executable may fail to run in the server if it is using an older version of version of GlibC than the one the application was linked against. Therefore, this problem may also affect ruby and python libraries written in C, C++ or Fortran. Other advantage is that docker reproduces entirely the development environment and encapsulates its configuration. So, docker also saves time that would be spent on manual system configuration chores, editing configuration files, creating symbolic links and so on. By using docker or any other container technology such as Podman from Read-Hat one can also get pre-configured and pre-made systems up and running quicker and also swap the configuration.

A reason, for not using docker would be when using any application written in Go (Golang) since Go static links almost everything and does not even rely on Linux GlibC (GNU C library), so an application built with Golan can even run in old distributions.