The table claims to be from a year-long survey of 1.2 million people with only a bachelor's degree.

I'm a bit biased, but in my experience philosophy majors tend to be pretty smart and philosophy degrees don't lend themselves to any particular career path. So I don't find it surprising that there's a big gap between where philosophy majors start and where they end up. And the initial number is probably especially skewed downward by lack of initial direction (I would have been ecstatic if my first job out of college paid $39k).