Renewed for final sixth season

Money. Contracts up after S6 so the studio, producers, cast would expect a pay raise which would mean an increase in the licensing fee to Netflix. Guess Warner Horizon and Netflix couldn't come to terms for beyond 6. Plus Netflix in the 2 years since it picked up Longmire their business plan is to produce more Original content in house with their own studio so they have global rights one of the same reasons A&E gave for cancelling Longmire after S3. Right now Netflix only has rights for Longmire for US, Canada, Australia, and New Zealand. Warner retains the rights elsewhere. Plus Longmire was on the low end of viewership numbers according to some sources I'd seen recently as compared to Netflix's other Originals like Stranger Things, OITNB, and House of Cards with more Originals in the works. Seems they made the call that there wasn't enough profit to continue past S6. At least we got 3 more seasons with Netflix. These days a series that runs 6 seasons is a good run. More than that is the exception not the norm. Netflix has also cancelled their Original Bloodline, S3 being it's last.

Yeah, I was hoping for 2-4 more seasons too, but I am pleased, that the cliffhangers will get resolved at least.