Americans Elect’s web page has this article, explaining why it is circulating a petition to qualify as a party in California, instead of using the easier registration method. California lets a new party qualify if it has registration equal to 1% of the last gubernatorial vote, or if it submits a petition signed by a number of voters equal to 10% of the last gubernatorial vote. Americans Elect is using the latter method.
Courts have unanimously invalidated ballot access petition requirements for new parties and independent candidates that exceed 5% of the number of registered voters. The California 10% petition has never been invalidated, however, because it is not mandatory. Groups are free to use the 1% registration method. The 10% petition method has been in the law since 1937 and it has only been used once, in the autumn of 1947 and the spring of 1948, by the Independent Progressive Party that ran Henry Wallace for President in 1948 (Wallace was a former vice-president of the United States). By contrast, since 1937, every other party that qualified in California has used the alternate 1% registration method. The newly-qualifying parties that used the 1% registration method are the Townsend Party in 1938, the American Independent Party in 1967, the Peace & Freedom Party in 1967, the Libertarian Party in 1979, the Green Party in 1991, the Natural Law Party in 1995, and the Reform Party in 1995.
Before 1937, groups could qualify as a party in California with a 1% petition.