Tired of it

I'm reading a Kevin Kerney mystery (Michael McGarrity) that I borrowed from the public library. Kerney is a Santa Fe, New Mexico, police chief who, as a series character, started swell and has become mired in personal troubles (kid-gloves wife). Death Song, as a novel, started swell and has become mired in political commentary, personalities, etc.

I wonder if the point where the reader gets tired of a book is the same point where the writer tired of it, too. I also wonder why any mystery writer thinks the reader is going to enjoy something as topical and banal as political potshots totally unrelated to the storyline.