#6 The Big Show
Let's be honest here.
The WWE Universe has wanted The Big Show to retire for years now, especially after enduring his constant heel and face turns, and 2019 might finally be when they get that wish. Of course that's not to wish the man any ill will or anything of that nature, its just that its hard to imagine WWE being able to do anything else with him.
Not only has he turned heel and babyface a handful of times over the course of the last couple of years, his immobility is making it difficult for him to even look like a threat anymore. Beyond that, WWE currently has him working as the muscle for The Bar, which can't last much longer with the fickle nature of the tag team divisions right now.
In the end, Big Show is getting up there in age, he's losing mobility and there really isn't anything else the company can do with him . If nothing else, all those signs point to him needing to finally hang up his boots and transition towards backstage role with WWE going forward.