while dexter has teetered on, jumped over and back and forth when it comes to shark, it had to come to an end sometime. showrunners said the following:
We wanted to end it this year, but the network convinced us that it would be best to do it in two years. In some ways, this is a two-season series-ender. We have worked that out and know where it’s going to end. Next year will definitely be the last year of Dexter. Absolutely.
go figure. [SOURCE.]