Pondering Underrated Writers

What makes a writer “underrated”?  I’m only asking, because apparently several writers I really like are underrated, and I’m not exactly sure what this means. I’m working with a few scenarios here, because I feel like the writers below could easily be classified as “underrated,” considering that people I think of as “big names,” like Deborah Eisenberg, Stephen Elliott, and Sam Lipsyte are on the list.

Example: if say, fifty people buy The Instructions by Adam Levin (god forbid), but it gets turned into a feature film starring Leonardo Dicaprio, is Adam Levin still an “underrated” writer?

Example 2: if less than 5000 people read Blake Butler but it turns out that Scorch Atlas is actually laced with code to cure cancer, AIDS, etc. is Blake Butler still “underrated”?

Example 3: if it turns out that Christie Hodgen is actually Philip Roth masquerading as a woman, so he can move away from his personal brand, is Christie Hodgen still “underrated”?

Somebody help me, help me!