>>50406983Pokemon was in his "dark age" (apparently started with R/S) during HG/SS release, most people discovered HG/SS way later than when it was initially released. Also gen 2 isn't that popular, most old players remember it because of postgame Kanto but no one cares about the Johto region.
BD/SP sold better than all the others remakes because Pokemon is popular again and gen 4 is massively loved (almost as much as gen 1), the D/P remake was way more hyped than its predecessors.