> why do people drink so much, to the point of drunkenness?

Many reasons. To the point of darkness because it's a thin line between a light buzz and over-the-top-cannot-even-say-my-name

> Why is this so common?

human nature. Not only human, actually, monkeys drunk on fermented fruit, etc [1]

> Has this always been the case?

Yes

> Will this change?

No.

[1] http://www.australiangeographic.com.au/topics/wildlife/2011/...