Couldn't that have also applied to Cody? Of the current-day roster, only a handful off the top of my head are guys that came up through the WWE system and learning strictly the WWE style. Ziggler, Corbin, Reigns, Strowman, and I'm sure I'm forgetting about someone (Orton fits, too). Reigns, Strowman, Corbin & Cena are protected... they'll never wrestle on the indies. Ever.
A guy like Cody was second generation, came up through WWE's system and only wrestled the WWE style and now look at him on the indies. I feel like Cody also applies as the "test case". Not saying Ziggler doesn't, I think the two of them were always those guys where they weren't so high on the card where they couldn't leave and were too big for the indies, but also guys that came up only learning the WWE style.
One has already had big success. If a second one went out and was successful, it wouldn't be good.
On that note, Joey Ryan bought a $525,000 house in LA with a pool and credited it to the change in the wrestling business where you don't need WWE to make a living anymore like 5 years ago.