Half of these exist because I was bored once.
The Windows 10 and MacOS ones are GPU passthrough enabled and what I occasionally use if I have to use a Windows or Mac application. Windows 7 is also GPU enabled, but is more a nostalgia thing than anything.
I think my PopOS VM was originally installed for fun, but I used it along with my Arch Linux, Debian 12 and Testing (I run Testing on host, but I wanted a fresh environment and was too lazy to spin up a Docker or chroot), Ubuntu 23.10 and Fedora to test various software builds and bugs, as I don't like touching normal Ubuntu unless I must.
The Windows Server 2022 one is one I recently spun up to mess with Windows Docker Containers (I have to port an app to Windows, and was looking at that for CI). That all become moot when I found out Github's CI doesn't support Windows Docker containers despite supporting Windows runners (The organization I'm doing it for uses Github, so I have to use it).
I run a different LXC on Proxmox for every service, so it's a bunch. Probably a better way to do it since most of those just run a docker container inside them.
Why mix docker and VMs? Isn't docker sort of like a VM, an application-level VM maybe? (I obviously do not understand Docker well)
I like to run a hypervisor host as just that, a hypervisor host. The host being stable is important, and also reduce attack surface by only having it as that.
An LXC per service is somewhat overkill. A docker host running on LXC could likely run all the docker containers.
I mentioned above, and not to spam, but there might be a use case that requires a different host distribution. Networking isolation might be another reason why. For 90% of use cases, you’re correct.