Sure, hubris is part of it.

You are also getting paid (hopefully - if you aren't, then you're really screwed). It's not a lot, but enough to live on as a single person.

Then, the academic humanities lifestyle is quite cushy for anyone who really loves reading, thinking, and writing. And as a Ph.D. student, you get to live it for 5 years or more. There's very little of the grant race (you just need a few thousand dollars a year to travel to conferences/archives), there's no grueling lab work. There's not much pressure to perform from your advisor, who is likely working on unrelated projects within the same sub-field. It's just reading, thinking, writing, and talking about other people's writing.