The thing about climbing the ladder is that the it only passes overhead every so often. If you don't grab that bottom rung and start up, it may be years before you get another chance to move beyond just "earning a living".
I think that's why a lot of the people mentioned in that article way up in this thread have dropped out of the game. They know that once they accept a job that allows them to "earn a living" they're ineligible for getting back on the ladder.
Okay, the metaphor is getting clunky. But the reality is there were times when I was unemployed and I didn't even look at the listings for the entry-level positions. Sure, I could have earned a living doing them. But it would have set me back years in my career. It's perverse, but it's more acceptable to have a several-month gap on a resume than it is to have a period of underemployment.