Ask HN: Why are developers paid so much more than system administrators?

I understand these are two different skill sets, but often you will find such people working in the same environment which is something I can observe for myself and the question begs itself: why are developers paid "so much" more than sys admins?

System administrators (or System engineers, titles have no meaning these days) have to make sure the entire infrastructure and all platforms are operational at all times and fix any unexpected problems on the spot. You need not just know how to restart Apache but know how to configure it, tune it, debug it and upgrade it without causing any downtime or as little as possible and that goes for databases, mail, storage, networking and not only superficially; you need to know these technologies inside out!

There is shift work, unpaid overtime, constant off-hours maintenance and the everyday stress of making sure everything is up and running and if it's not then "you need to fix it right now or fired". None of that concerns them (developers). The vastness of skills required is much larger than that of a developer so as I observe them not having to do half the stuff I have to do while getting paid 30-40% more on average (my observations in my company and by looking at jobs online) I can't help but ask why? Is their value really so much higher? I want to know what other people think about this.