The point of writing software isn't to maintain it forever

Exactly. And the example given (cron) was designed with the Unix-mentality of writing a program that does one thing really well and does it without breaking. Yeah, sure, some may argue that cron is fairly complicated, but it doesn't suffer from the maintainability needs of a very complex piece of software like some enterprise systems.

Is it though?

Take this example, there's really no reason for me to do anything EXCEPT that the upstream dependencies have been yanked. Now I need to do a bunch of porting.