Because the last entry in the main series was in 2008 (Size Matters/R&C 5).
The rest have been spin-off's ("Future" Series, A41 etc).

However, Ratchet & Clank is getting a huge feature film, that will do wonders, with a brand new PS4 game. And if the PS4 game is as good as all the other games in the series, expect greatness.

Remember, Nintendo's most "Acclaimed" game used and borrowed a lot of elements from Ratchet & Clank.
To the point, that Miyamoto said he'd never heard of "Ratchet & Clank" when the comparisons came out, even though he'd acknowledged it in the past. So let's not.

Yes, the world needs Metroid Prime 4.

mess, I remember him


Teach them!

He's right though. And it's also clear from play these shooting games that the game developers focus on graphics much, much more than the actualy gameplay. Most of these games look realistic but are quite boring, whilst most Nintendo games don't look realistic but are fun. On Xbox and Playstation they only have a few games like Tekken and Crash Team Racing and things like that where the focus is on gameplay over graphics.