I'd rather watch a 2 hour movie than watch a long drawn out TV series.
If a TV show does not get high ratings right away it will likely be canceled during or right at the end of the first season!
Odds are if you were one of the faithful few watchers you would have become emotionally invested in a show without a resolution.
On the other hand if the show is a raging hit then the network wants to hold onto to it for a minimum of 5 years which will guarantee reruns in syndication. Some shows like the original Law & Order was on for 20 years and it's sister show Law & Order SUV has been on for 15 years. These shows however have a different storyline for each episode.
Attempting to tell (one) story over the course of 5, 10, 15, or 20 years is bound to lead a lot of people to fall by the wayside.
In my opinion the best TV show to ever pull off the (one) story show was "The Fugitive" which aired on ABC from 1963 to 1967.
The 1967 final episode of The Fugitive, attracted a 72% audience share when it was broadcast!
However keep in mind most people only had 5-9 TV channels to watch back in those days. Most people only had one television and it was in the living room. You also couldn't DVR it or watch it "On Demand" at a later time and VCR/DVDs had not been invented.
Today there are hundreds of cable TV stations in addition to ABC, NBC, CBS, and FOX. People are also watching original TV shows produced for Netflix and Hulu. It would be a real challenge to maintain a TV series based on one storyline/book these days.