Political/career opportunism, just like she decided a couple years ago to run for mayor on from her PTA position, then run for Gov. Gotta remember these people who are politicians, that's their job, so it would be like every 2 or 4 years you having to run or campaign to keep your own job. Then 'moving up' like getting a better job within a company (or a raise) would be to them going from mayor to the house then the senate etc.
I'm a cynic when it comes to political ploys, I saw her pick as a ploy to get Hillary supporters which if the case has backfired. Apparently McCain was going to pick Lieberman which would have split the Republican party in half (the christian right, theocracy types wouldn't of shown up otherwise. If you are a Republican you cannot challenge the "Moral Majority" Focus on the Family types). The Republican big wigs said if he did that it would be suicidal to the party. So in McCain picking Palin as she represents the party's base beliefs in order to get people excited about the 'Republican brand'.
So Palin's pick really shows what's wrong with American politics. I knew a guy in college back in the states who is a gay black republican. He always said he wanted to vote for the Republicans on economic issues, but obviously as a gay black man he couldn't vote for that party, since they are fundamentally opposed to his existence.
Or the other classic example is a 'New England Republican' which is socially left, economically right. That doesn't fit in the Republican party. Democrats are a bigger tent, they control Colorado, Wyoming, Montana, New Mexico, North Dakota, Arizona by running more liberatarian types.
Then on the west coast a Republican is a social left or moderate economic moderate. In the South a Democrat is a social right/economic moderate. Then in the Midwest its a civil war because all the midwest states straddle the southern way of thinking(conservative) and the Northern Midwest (liberal) way of thinking.
hope that makes a little bit of sense.