We have this at my work, need to totally gut the main product offering in order to maintain long term viability but nobody will do it because it's the cash cow even though it's slowly dying.
This is a strawman. You're extending their argument to an extreme so it sounds silly when it's not what has been proposed.
The argument is clearly to keep direct dependencies required for building in source control so that if you have a working build system, you can build the software indefinitely and independently from the internet.
Build systems and operating systems don't disappear overnight. Leftpad does.