I think it is a matter of "opportunity cost". If you take the commute as a given then the question wrt to the technical tome is: "What must I give up to read this book?" On the train the answer is: "Sleep, stare out the window, solve crossword".

Contrast with home where the answer is: "anything and everything." Then reading a giant technical treatise is not quite as appealing an option.

I'm not advocating long commutes but there is perhaps something to be said for artificially limiting one's choices at times.