'When people did help they were given a flattering name. They were "editors" '

From: How I fell in love with Wikipedia

It was like a giant community leaf-raking project in which everyone was called a groundsman. Some brought very fancy professional metal rakes, or even back-mounted leaf-blowing systems, and some were just kids thrashing away with the sides of their feet or stuffing handfuls in the pockets of their sweatshirts, but all the leaves they brought to the pile were appreciated.

And the pile grew and everyone jumped up and down in it, having a wonderful time. And it grew some more, and it became the biggest leaf pile anyone had ever seen, a world wonder.

And then self-promoted leaf-pile guards appeared, doubters and deprecators who would look askance at your proffered handful and shake their heads, saying that your leaves were too crumpled or too slimy or too common, throwing them to the side. And that was too bad. The people who guarded the leaf pile this way were called "deletionists".

But that came later. First it was just fun.

Wikipedia flourished partly because it was a shrine to altruism. It also had a head start: from the beginning the project absorbed articles from the celebrated 1911 edition of the Encyclopaedia Britannica [4], which is in the public domain. And not only the 1911 Britannica. Also absorbed were Smith's Dictionary of Greek and Roman Biography, Nuttall's 1906 Encyclopedia, Chambers' Cyclopedia, Aiken's General Biography, Rose's Biographical Dictionary, Easton's Bible Dictionary and many others.

But the sources and the altruism do not fully explain why Wikipedia became such a boom town.