I think that's mostly because he had a start to finish plan mapped out for the story, perhaps he just wants to have the same thing mapped out to continue it. #19 with the first glimpse of TOAA and OBA Bruce had TOAA cryptically listing off all the arcs of the series. That's probably also why Gamma Flight is becoming a thing, since it can probably explore just more singular issues and whatnot rather than turning Immortal Hulk into a write as you go plot, plus it's almost guaranteed Ewing wouldn't hit roadblocks by editorial if he presented the entire plot and the hype was still strong after a break of Immortal Hulk stuff, then compared to maybe not having a story completely fleshed out yet, meandering and hype for the series nosediving with fandom calling for his removal off the book, etc etc.
I have 100% faith in Ewing though, I really doubt were anywhere from seeing Immortal Hulk and its cast disappear from spotlight, just Ewing taking a small break but still using all the characters. The Teen Brigade is still around, Namor is also teased to be in Defenders and we never saw what their plan was in #25, these are all things that can be looped back around to when Ewing feels like it, and hes not a writer who leaves a plotline unresolved without intent, the plot of Empyre was originally set up in his New Avengers run, 4 years prior to the actual event.