There have been a number of historical articles written about it (the best one in my opinion is Paul La Farge's Destroy All Monsters—but there are lots of others) But I really think the issues were money, who got credit for what, and the fact that these guys were not located in the same area—distance leads to difficulty in communication, and Gygax was trying to run a business as well as be ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.