The real reason for the drop in history majors is that students and parents refuse to believe your last line is true: “History majors’ median earnings are higher than other college graduates’”
As that @benmschmidt piece notes, there were still *plenty* of majors through 2008. Something big happened to the economy around then, I think?
It’s always — always — some version of “my parents want me to get a STEM degree so I can get a job”