Why did Veronica Mars series end in the 3rd season? I found the plot of the whole series really nice and interesting. I'm gonna see the movie in the next few days but it seems unfair to end like this...not knowing what happens between Piz and her, how Vinnie Van Lowe is elected sheriff, how her dad clears his name or continues his life, what she does as an intern in FBI...
Because of low rating, it got critical acclaim but it lacked in attracting more viewers. So it got cancelled after 3rd season by The CW.
A group of fans calling themselves the "Cloud Watchers" sent more than 10,000 Mars bars to the CW, hoping that the network would reverse its decision and renew the series. (Source: Wikipedia)
The movie was made only to give closers to the unanswered questions. Even Warner Bros. said no to produce the film, it was Kickstarter fund-raising which made it possible.
Here is the creator's word on the whole story.
Note: So if you want to complete the story you need to watch the movie after the 3rd season.
As BCdotNET said there is a Season 4 teaser made for an attempt of making season 4 but this teaser is became non-canonical because of movie’s story conflicting with it.