Why so, though?

The usual hype curve that everyone should be using it no matter what kind of workloads.

Not really. Containerization has clear and obvious advantages over the traditional bare-metal approach.

For security purposes as used since the early days in mainframes and big iron UNIX, surely.

As workaround for broken dependency management, not really.

Whats the alternative?

Fix the dependencies story in what concerns Ruby and Python.

Native binaries can easily do with static linking (fix glibc or replace it with proper libc like musl).

Other platforms are doing quite fine without containers.

I kind of agree with you.

But in the Linux world no one has the intention to fix the package distribution problem except for that AppImage guy.