DP remakes won't happen because they would have to completely ditch the grid-based format of the originals and rebuild Sinnoh from the ground up as a new region.

ORAS was still limited to the grid layouts of Gen 6, and LGPE was LGPE. With Sinnoh remakes, they'd be using the Gen 8 engine, and Game Freak isn't willing to put in the effort to reimagine Sinnoh.