Are all viruses only capable of corrupting Windows files? Why can't they do the same to Linux?

And that's precisely why they can't – read Vikhry's post. Firstly, it's due to the clear separation of access rights. Because in Linux, no program can control the machine independently and secretly from the user; this system won't do ANYTHING until you tell it what to do.
But in Windows, any program can launch itself with system privileges – and nothing will stop it, because there's nothing to stop it – how can the system prevent itself?:D. That's how it happens that 3 scripts in VB, with a total size of one hundred lines of code, and one binary file of a few kilobytes can consume hundreds of megabytes of RAM and gigabytes of hard drive space, change several dozen (or even hundreds) of registry parameters (as is well known, this is one of the most important "parts" of Windows) – from harmless to critical – this is how the well-known and terribly annoying Brontok worm (also known by other names) works. And I recently saw the code for these scripts – it's just funny, to be honest.