I'm not a fan of 'only Game Freak knows' answers, but only Game Freak knows.
Gen 4 came out on September 28, 2006, nearly 10 years ago. While this is quiet a while ago, it's actually only 2 gens and a couple games series ago. In terms of amount of Pokemon releases, there isn't that many after DPP (especially Platinum, since it came out a year later). Gen 4 is still quite fresh in people's minds. Whether or not it already deserves a remake, we're not sure. Hoeen remakes were long overdue, and FR/LG we're most made to resell their popular game on a better console with updated features rather than an actual remake, an issue that isn't prevalent for DPP.
It's still more than possible for a DPP remake, it's probably likely, but it's not something that has been majorly requested for nor is needed right now.