Hollywood script writers/developer's love of the dark hero/antihero. It became a hit theme with The Crow and "dark Batman" and so forth in the 90s, and by the time Dexter came along, it seemed everything beyond it was no longer in the thought process for any script development.
Whatever you thought of Dexter for its early seasons, you could feel it slipping away by season 7, and for this final season, it became evident the series had overstayed its welcome. The writers seemed to be throwing darts blindly for potential plot points at random, and "yeah, that could work, let's go for it." The entire premise of Dexter Morgan's character and "code" had eroded by S7, and the series was now hurtling recklessly toward what has been dubbed one of the most disappointing series finales of all time.
It was always a stretch, to put it mildly, to reason Dexter would worm his way out of most of the messes he had been written into. But of course he had to escape without repercussion, he's the lead dude, right? But the morph from the end of S7 to the start of S8 {"6 months had passed"} was inept and absurd.
Characters are just lost here. Past development now leads to nothing. Batista seems a mere shell of himself. Joey is a cardboard cutout, standing around in scenes with nothing to do. Jamie, one of the few remaining likeable characters, we dont know what to do with her either, so hey, lets have her and Joey doing the bedroom bump every 20 minutes. Lazy and weak.
Charlotte Rampling was an accomplished actress but this story line with her materializing from Dex's past seemed very ill conceived. And Debra, whose foul mouth became tiresome before season 1 had ended, now a train wreck, has lost all her appeal. Really there was - by this final season - no one to care about.
I suppose if Dex had gotten his comeuppance or they had explored more intrigue in that direction, an 8th season might have been worth a look. Instead, it was just confirmation that the show was, by S8, about as fascinating as that old drunk on the park bench: Rancid, unappealing, and best avoided.