Wild culture! At almost[1] every (non game) software company I've ever worked, the source code was sacrosanct. If nothing else in the company was backed up, controlled, audited, and kept precious, at least the source code was. The idea of just casually deleting stuff because you think you're done sounds crazy to me as a software practitioner.

I still have backed up copies of the full source code of personal projects that I wrote 25 years ago. These will probably never be deleted until I'm dead.

1: One company I worked for didn't have a clue about managing their source code, and didn't even use source control. They were a hardware manufacturer that just didn't understand or care about software at all. Not what I'd think of when I think a professional game developer.

Spite and retribution is a thing. EA acquired C&C