What is the point of listing 1000 authors for a single scientific paper? I arrived at the printer room this afternoon to collect my printing and I happened to notice that someone was yet to collect a printout of the gravitational waves paper that has been all over the scientific news the last few days/weeks. Of course, I was curious, so I had a peek.

It struck me that there was only one author... until I saw the asterisk indicating a full list of authors could be found at the end of the article.

There I found three full pages of authors. I have no intention of counting the exact number, but a quick estimate by word count suggests there are over 1000 authors from 133 institutions.

You always need to give credit where credit is due, that is a given. But to put it in context, there are at most 7 words of article per author. In fact, I can think of a number of problems coming from so many authors (like who do you contact if you have a question - the list is alphabetical and there doesn't appear to be a designated contact person).

What is the value of listing so many authors and why should (or shouldn't) it happen?

Update:
Thanks everyone for the thoughtful answers. As much as I want to choose an answer, I honestly cannot decide between the two most upvoted, so I'm going to abstain from choosing one.
The "point" of 1000 authors is to recognize that 1000 people contributed to the paper at a level sufficient to be considered authors, according to the standards of that particular field.

In some fields (including high-energy physics), large numbers of authors are not unusual. See e.g. the 2015 paper estimating the mass of the Higgs boson with 5,154 authors. This kind of research often involves very large teams spanning multiple institutions. Typically papers published as a result of a collaboration are credited to all members of the team. 

For more information see Report by the Working Group on Authorship in Large Scientific Collaborations in Experimental High Energy Physics.