I think the main problem is that gamers are lazier than before and instead of researching games they just go "well I know Mario, those are always fun." ditto with Zelda, Pokémon, etc. And so those are always the ones that sell. Video games have just been around so long that the older casual gamers have gained a comfort zone and have a harder and harder time stepping outside of it as they get more real life responsibilities.
I'm kind of guilty of it myself, but I do step out of that zone by saying I also want to try all the new RPGs. That should get me a lot of unknown franchises right? The problem is that RPGs usually aren't ready for consoles in large quantities until later in the systems' lives. I'm sure they helped boost the PS3 a lot in later years.