What does it mean to be "lazy"? Why are some people lazy, and others not? Why are people lazy with regards to certain things and not others?

Ignoring all of these questions and simply considering laziness to be a fundamentally characteristic is highly unsatisfying and, dare I say, lazy.

Maybe the authors explanation is wrong, but she offers a potential explanation. Your proposal is simply that 'she is lazy because she is lazy' which offers no explanatory power.