The problem they have is a simple one, but one not many fans will appreciate.
Ryan Reeves was in developmental for a LOOOONNG time... nearly 7 years in total, he has bounced in and out with injury but ultimately, they have a lot of time and money they invested. But it's the "old way" of doing it and frankly, it didn't work with him.
Those from that original NXT format of the show and developmental who progressed in the ring and on the mic reached the appropriate level for their talent. Bryan, Barrett, Bray Wyatt, even Heath Slater and Fandango and the Prime Time Players all benefitted from the experience, even if they are not World champs yet, all are valued members of the roster. The ones who didn't very quickly found themselves either cut or relegated to the midcard/jobber status. Axel was there for a long time before his rebranding, David Otunga is still employed as he can work Legal and they don't want to upset Mrs Hudson and her Hollywood buddies but hasn't been seen on screen for a long time... Bateman/EC3, Cottonwood, Tarver, Kaval... they all are long gone.
Of all of them, Ryback was the one Vince would have been desperate to get over... look wise he had the best of the original and New Nexus other than Barrett and was given that big push once his injury healed up... but he is still, after 7+ years in developmental and 2 on the main roster being pushed, the utter shits in the ring. He hasn't grown or progressed and is considered dangerous by many of his peers.
Add to that his attitude has been called into question several times through his actions to the media... It's frankly amazing he is still employed when some talents like Tarver, who didn't do much wrong other than not click with Cena got canned or Tyler Reks realised he wasn't gonna make it and went home...
Since all those guys came in they have a massive investment in the new Performance Centre and training system and it is working...it's proven itself already. Not one talent who has stepped up to the main roster full time has failed since they had NXT and the PC in it's current form. Their new model is to take the top indy guys, spend a period in NXT and the PC and then they immediately step up to be major players. Not bit parts but major.
Ryback didn't make it to the level he should have and for them to put him ahead of these newer NXT graduates, if he hasn't gotten better undermines the whole programme... Rusev has already done more than Ryback managed in 2 years of push... its also a slap to a Barrett, Wyatt, or Slater-Gator or even Axel who came through the same system, took their chances and are better now than they were then. Ryback is injury prone... Barrett isn't, he has just been hurt by others twice... Ryback gets hurt a lot AND hurts others... a bad combination for sure.
It's on the bubble for Ryback, there is an argument that says he should get one more crack at it... and one that says he blew it and he's better off headed to GFW or Japan or even TNA. In either Jarrett or Dixie-Land, He is a player... not quite the CM Punk that TNA want, but he'd be a steal in their eyes and someone who could do good things for GFW as one of their top 6 guys. In the WWE where realistically can he now go? How many guys are actually ahead of him in the pecking order through their hard work...and what damage can be done to their burgeoning developmental if a failure like Ryback is put ahead of them... or genuinely talented guys like Drew McIntyre who got released. What happens if they make a big signing like a Devitt and Ryback hurts him first time out?.
Has Ryback been missed on WWE TV? Not really, I barely registered he was gone... add it all up and with the kind of guys they have coming up soon and potentially coming back then time to cut bait with him as the failed experiment he is... I'd rather see a Matt Morgan return in that role than Ryback get more chances... he hasn't earned them over other guys...