I have no idea why…

This have to be installed manually because it's only needed to build Docker images correctly.

Containers cannot update shared volumes from new image versions

This is to force update of static files if mounted from a host volume.

Poetry 1.0.0 has been released 

This is needed because when updating an existing environment, the
existing volume will shadow away the changes done on container build.

Eases deployment, especially on hosters that charge per volume.