It was generally assumed that with five defensive tackles already on the roster, either Cullen Jenkins or Markus Kuhn would be waived to make room for Nix. The Giants, evidently, decided to go with option C "None of the above", and cut free agent signee Kenrick Ellis.
Ellis was expected to add depth as a run-stuffing defensive tackle to a defense that desperately needed to upgrade their run defense. He was signed in the "second wave" of free agency to a one year "prove it" deal after being let go by the New York Jets.
This brings up several questions.
1) Why Ellis?
2) Why not Jenkins or Kuhn?
We'll start with the first question.
The simple answer is that when Nix is healthy -- and we should assume he is --, Ellis is redundant and outclassed. Louis Nix not only brings Ellis' ability to clog running lanes and control blockers, but he also has the power, quickness, and agility to provide some interior pass rush (even if it is "collapsing" the pocket rather than "penetrating" it).
Also, Nix is in the second year of a rookie contract, which puts him under the Giants' control for longer and less money than Ellis' one year "prove it" deal allows.
There could also have been personality issues in the locker room that we aren't privy to. That sort of thing might never come out (particularly with a team like the Giants), but it does happen.
Now for that sticky second question.
First off, Jenkins is a veteran. The Giants are going through a major youth movement at the moment, but they still need guys in the locker room who have "been there and done that". Jenkins provides leadership and mentorship to the young players, helping to settle them down, slow the game down, and help teach them how to prepare like professionals. Also, while his decline from the second half of 2013 through 2014 shows that he is no longer an every down player, Jenkins does offer ability as both a defensive tackle and defensive end in a more limited role. That kind of versatility is definitely useful.
And as for Kuhn?
Honestly: I got nuthin'.
Throughout camp and the first part of preseason, I figured that Kuhn was getting chances to show the coaches something, anything, to keep him, but ultimately wouldn't make the roster. I don't begrudge that to the coaches, after all, Kuhn is the kind of high-motor, high-character player that coaches love to have. But I never saw anything on the field. His best game was still overshadowed by the other defensive tackles on the roster.
Perhaps the Giants are rewarding Kuhn's hard work. Perhaps they are keeping him around as an example for the younger players to show the merits of hard work. My personal conspiracy theory is that Kuhn is actually an unblockable-man beast, but has been sandbagging it in preseason to throw off offensive coordinators.
But then there's this from Tom Coughlin:
"Well, he's a big, strong guy. We've talked an awful lot about stopping the run, and he can hold the point in there, which he's done over and over," Coughlin said. "He's very smart, and so we look at him as a guy that can anchor down in there and can knock back off the ball. And he's pretty much done that."
Somebody in the Giants organization obviously likes Kuhn. Tom Coughlin has stood behind his player in the media, but he stands behind everybody. Is it Steve Spagnuolo? Jerry Reese? Whoever it is, hopefully Kuhn will -- finally -- reward their faith in him.