The RPG genre is starting to merge with the FPS genre. Most RPGs are now First person, as opposed to it's previous Top-Down (Baldur's Gate), Real Time Strategy (Warcraft 3, Turn Based Strategy (Final Fantasy, and Action-Adventure (Too Human) phases. RPGs aren't a genre on their own, and so, when a new base for the genre becomes popular, they're often unrecognized by RPG fans to be RPGs. They aren't disappearing, they're hiding. Thank Bethesda for making the latest transition, albeit Valve was doing FPRPGs (First Person Role Playing Games) before it was cool...
In your case, you relate RPG to TBS (Turn Based Strategy) games. The reason they're dying out, if they are, is that it was a simple gameplay mechanic designed for more primitive games and engines can support more exciting gameplay nowadays. Turn Based Strategy Games are probably destined for handheld systems... the two most popular franchises in the industry, Final Fantasy and Pokemon are both now on handheld games.