
This post was inspired by a compilation video of Gohan's entire screentime in Daima. Unsurprisingly, it amounts to less than 50 seconds, consisting entirely of (very well-drawn) flashbacks to the Buu arc and one of the show's intros.

Can't wait to never see half these guys in the show...
Now let me make one thing clear, I wasn't desperately craving a Gohan appearance while watching Daima. Some held out hope for him swooping in at the last minute to help against Gomah, or some other fan-pleasing twist involving the return of Teen Gohan® (SS2).
No, the writing was on the wall when we didn't so much as get a glimpse of Gohan's Mini form. They provide the tiniest piece of lip service that he's concentrating on studying after the Majin Buu crisis, which is pretty much Gohan's equivalent of "he's hibernating again".
It feels like choosing beggars to argue that Gohan is in any way underexposed in modern Dragon Ball after he and Piccolo got an entire movie in the spotlight. He got his long-awaited "big win" over a main antagonist, a shiny new transformation, and the promise of continued relevance in future projects. But it's common knowledge that Gohan was not part of Toriyama's original story outline for Super Hero, which is in hindsight quite evident.
Beyond the repeating cycle of Gohan neglecting his training and having to regain his fighting instinct which we'd seen time and again, Gohan doesn't get anything close to a real character arc. If anything, Toriyama seemed to go out of his way to portray Gohan as negatively as possible, maybe even more so than his father often is. On top of his usual complacency, Gohan is portrayed as selfish, neglectful of Pan, and comically oblivious to everything going on. You're basically rooting for Piccolo to slap some sense back into him the entire time he's oversharing about his ant hyperfixation.
All that is to say that Toriyama agreed to include Gohan, and even threw him some bones, but it felt... almost begrudging. Therefore, it came as no big surprise that Gohan is absolutely nowhere to be seen in Daima.
I think Toriyama's apathy - bordering on antipathy - for Gohan boils down to his perception as a boring, static character, hence deeming him unfit for the protagonist role way back in the Buu arc. Gohan is not interested in fighting or adventures, so unless he is literally dragged along or forced into action somehow, there's not much that can be done with him. Of course, it's hard to ignore that Gohan is one of the strongest characters in the setting, but this lofty status almost feels like an unwanted fly in the ointment of the stories Toriyama actually wanted to tell... stories that were written with Goku in mind, not Gohan.
I guess Toriyama was a bit like Agatha Christie in that he grew to dislike the traits of some of his own characters, but he's so committed to keeping them consistent that he won't arbitrarily change them. To quote Christie about her most iconic creation, Hercule Poirot:
But whereas Christie powered on with Poirot as her hero, Toriyama's approach to Gohan is to simply means keep him out of the picture as much as possible."There are moments when I have felt: Why-Why-Why did I ever invent this detestable, bombastic, tiresome little creature? …Eternally straightening things, eternally boasting, eternally twirling his moustaches and tilting his egg-shaped head… I point out that by a few strokes of the pen… I could destroy him utterly. He replies, grandiloquently: “Impossible to get rid of Poirot like that! He is much too clever."
From this post, you might assume I hate Gohan's guts, but I don't at all. I'm merely trying to think about this from the creator's perspective, as I imagine it.