Look at it this way.
In the past generations, remakes fit due to the chronology
Ruby/Sapphire were set at the same time as Red/Blue, as referenced by various things in regards to Kanto and TR - Remakes made
Diamond & Pearl were set at around the same time as Gold/Silver, 3 years later, as referenced by the news report about the Lake of Rage at the start, and more TR references.
Black & White, however, are set 5-10 years after DPtHGSS so having RS remakes wouldn't really fit the series chronology