OK, as a political scientist, I should be able to answer this question. And the answer is, there are multiple answers. In no particular order:

1) The barriers to entry are low. In modern American politics, the barriers to becoming a candidate are daunting. There signatures to collect in order to get on the ballot, party primaries to win, money to raise, and a lengthy campaign season.

Contrast this with the California recall election. Getting on the ballot required only some paperwork, "65 validated voters' signatures and a $3,500 check" according to USA Today. There are only sixty days to the election. There are no annoying party primaries. Why, it would be stupid not to run!!

2) The barriers to winning are also low. Because of the plethora of candidates, many of which are trying to cater to the same voting demographics, it is highly unlikely that the winner will command a majority. True, at the moment, Schwarzenegger holds an early lead in opinion polls. If, however, his balloon were to burst, then the winner might only need 25% of the vote.

3) Publicity. California founded the celebrity culture, and as publicity stunts go, running for governor is on the cheap and easy side of the spectrum. Running for governor is a way to get or keep one's name in the news.

It works, too. When was the last time you thought about Gary Coleman? Think about this from Coleman's point of view -- what's the more dignified route to jumpstart a career, running for governor or celebrity boxing?

4) Horse-trading. Because the threshhold for winning is lower, any candidate that attacts a loyal cadre of voters equivalent to a few percentage points in the polls might be willing to throw his/her support to a major candidate in return for something, be it policy or patronage. This is how it works in parliamentary democracies in which there is a low minimum level for winning a seat, i.e., Israel. Expect to see this in California around late September.

Think about it -- two months of politicking in return for a plum job or a coveted policy shift? Not a bad rate of return in politics.

5) You could win. Jesse Ventura was not considered a serious candidate when he ran. Howard Dean was mocked when he decided to launch his bid for the presidency. You never know when lightning strikes.