Because they dont need to. Why should they spend money on a franchise that is already globally known and is one of the top selling toy brands? Thats business-stupidity.
You said that exact thing earlier, and it was just as stupid then as it is now (with all due respect). It would be business stupiditu NOT to promote the show. You can't expect people to just find the show on TV if they don't even know it's still on the air. Have we gotten ANYTHING in terms of a promo, even just a "Power Rangers RPM is coming soon," with only two seconds of all-sentai footage?
The way KRDK encodes have been trickling the safe bet would be that; you know damn well you can pop on later in the afternoon and have no less then 3 RPM links to choose from.