I guess they couldn't back-fill it? Which makes you wonder, what did they do with all the drill cuttings?

Science. The article: "The most intriguing discovery made by the Kola Superdeep Borehole researchers was the detection of microscopic plankton fossils four miles beneath the surface of the earth." and "The Kola Core Repository in the nearby town of Zapolyarny displays rock samples obtained during the drilling operation"

Unrelated: what surprised me reading http://en.wikipedia.org/wiki/Kola_Superdeep_Borehole was that a more recent borehole drilled 10 km (horizontally) within 36 days. That's over 10 meters an hour, kept going for over a month.

Falling in wouldn't be very pleasant, I suppose. :-)

There was a reddit comment where someone wrote, in poignant and graphic detail, about the slow death you would find if you fell in the hole.

Someone else replied, pointing out that the hole can barely fit your leg. The juxtaposition was pretty funny.

It's less than a foot wide. You'd probably be more likely to trip over the rim.

That's a long fall, 3/4 of a minute if I'm not mistaken.

120 miles per hour is terminal velocity of a falling human being.

120/60 = 2 miles per minute

Skydive fall from 15K feet is over a minute free fall.

Repeatedly bouncing off the edges would probably slow the fall, and make it significantly more painful. That is, if the hole were wide enough to fit you.