And if they end up serving no practical use they end up discarded and ignored by scientists and engineers (if maybe not pure mathematicians). The author's point is that there is no such selective pressure on lit crit.
Practical use ≠ commercial use! Also, I have no idea where you got the idea of "disgarding" research, especially in regards to pure mathematicians. What is "practical" to you?
Also, poststructuralist lit crit is not the be all and end all of "the humanities".
No, it's not, and yet when I deconstructed the author's paper (I crack me up), I found that he made a generalization about all of the humanities following his limited experience with the given topic.