Because when you turn the water off it's cold. I would rather pay 1.5 cents to remain warm while I lather. If the resource was actually scarce, it wouldn't cost so little to use it.
What makes you think that? How do you know they are reading Facebook and not reading the papers? From what I've seen on HN, people commenting contrarian studies have actually read them.
There's a whole lot of people in here trying real hard to justify why forgetting things about your craft is good. Guys, I understand memorizing is hard, but can we drop the ego a bit and just admit to ourselves that yes, we would be better developers if we remembered the standard libs? It's not strictly necessary nowadays, but it has not stopped being a useful edge.