Why shouldn't you get Linux from GetMyOS.com?

There are numerous reasons. I have tested the website, and it has been safe for me, but that is from my experience. I wouldn't trust anyone on the internet, and some of these websites can screw up your computer if you don't know what you are doing. The majority of them are safe, but you have to exercise caution especially when downloading software, like in this case. It's not only that however, the overwhelming majority of Linux distributions are open-source. This means two things. You shouldn't be downloading from websites that you cannot verify have the real software, and you should be downloading from the developers of the software, typically from their own websites. With GetMyOS.com, you don't exactly know those who run the website, and although they seem good, they are not well known and therefore cannot be trusted as much as the official publishers of these operating systems. Most Linux distros have official websites anyway, you can easily download image files of Ubuntu, Mint, Debian, Fedora, Arch, Pop!, etc to give examples. Search them up, and find the official websites.

The only reason you should download Windows image files from there is because, especially with older versions, they can be found easily and are probably safe to download. I would get the more modern versions (7, 8, 8.1, 10, 11) on the official Microsoft website, but

I am not a security expert. Let me state again that you should not trust anyone on the internet.