Longmire fans were given a shock when news came out that the sixth season of the show will be its last. The news was confirmed by Netflix. They announced it while the fifth season was ongoing. We know that Netflix doesn’t release viewing figures, so it is difficult to know the exact reason behind the ending of the show. The three main reasons for the cancellation of any show are— finances, viewership and the writers thinking that it is the correct time.
When you take a look at the novel series on which Longmire is based, you will see that it has covered the majority of the novel. So, in my opinion, after some deliberations, they decided that it was not suitable to keep on going with the show as they might run out of ideas and this would lead to the waste of resources. So, the showrunners just decided to end Longmire after season six.
The show originally aired on A&E. A&E canceled the show after three seasons, and the fans were stunned by the decision as the show left them on a cliffhanger. Netflix ended up picking the show for another three seasons. It is very unlikely that the show will be coming back now as they gave it a proper ending.