Honestly, I don't know why everyone expects remakes at all. They only made ORAS because of popular demand, and yet this gen they've made abundantly clear that popular demand isn't a focus anymore. And remaking Sinnoh isn't going to be as easy as you think it is. Those routes were designed with small sprites and tilesets in mind, and making them into 3D is either going to make them extremely cramped like they were in Alola, or else just be empty spaces with nothing filling them.

Personally, I don't care either way if they remake Sinnoh. DP were my least favourite games in the entire franchise, so if it never happens, nothing of value was lost to me. But if they are going to remake it, it can't just be another ORAS situation where they put the original game in 3D and add reference to the new mechanics. There needs to be actual effort to bring Sinnoh into 2020's standards, not just into 3D.

...and no, Dynamax isn't going to be in them. They couldn't be more explicit that that's a Galar-exclusive mechanic.