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).
On the joke, define "sane". 😬
On a serious note, I think there are valid reasons to have several VMs other than "I was bored". In my case, for example, I have a total of 7 VMs, where 2 are miscellaneous systems to test things out, 2 are for stuff that I can't normally run on Linux, 2 are offline VMs for language dictionaries, and 1 is a BlissOS VM with Google programs in case I can't/don't want to use my phone.