Are they really that desperate to get on to new technology and new video game consoles, I don't get it, right now they have about 220 million home console out there, that's huge potential for a lot of game sales for the developer, starting a new gen would be like starting out new with there games, the install base would be so low that it'd take quite some time for there games to sell really high numbers, they would have to be sure it's REALLY good to sell well on a new system.

Can someone explain why they're so desperate for next gen??

Cause it never lasted this long in any console gen. People expect the next wave. Furthermore, its become boring.

I know : now that the graphical boundaries of console have been more or less reached, developers can't impress the crowd with spectacular graphic evolution. So players will expect innovative features/gameplay/new IPs and devs don't like that because it's too risky. They're happier releasing their CODs, ACs, etc on new systems to avoid that.

Newer technology out there, more ram and bluray. Multiplatform console games are still limited by the ancient dvd.

Every Developer and Gamer except the Call of Duty Dev and people who play this games are desperate to show and see their new technology.

Nearly every studio(except the CoD DEvs) wants to show of their new Engines and so on.
They could go to PC of course but 95% of them can't sell stuff there - New Consoles will be bought time after time,thats a given especially if Developers put out good software.Epic is testing their Unreal Engine 4 with its 1st game on PC even if they said they dont like the PC the whole Gen...There comes the time even haters have enough of weak hardware especially if they use technology that was already old in this Gen(DVD)
Even the PS3 with its 600$ could sell enough to have games on there even if it took time for the console to really got into the game.

The same reason Sega and Nintendo made successors to the Genesis and the Super Nintendo.   Times change, technology evolves, and people want something new. 

This has already been said by someone in here (at least I think I read it here), but: developers can't get as good sales from shovelware/crap games at the end of the gen than they can at the start. Like Ryuzaki said, there's not as many wows to be had from graphical improvements this late on (though, Naughty Dog continue to impress), and just generally you can release poorer quality games that would get better sales.

Its getting harder and harder to impress the audience with better graphics. And with the limitations of the available ram and the high bar set for graphics eating up all available cpu/gpu time it's hard to try any new game play innovation.
Plus the huge 2nd hand market available by now for the current gen consoles and people starting to get lured more and more to pc where you can get games for under $10 that perform and look better I can see why they want new consoles.

Second hand games and consoles hurt sales much more at this point into a generation than in the first years. Game developers want to sell games, so they don't want hundreds of great and cheap games competing with their new games.

The sales of the games and consoles are not doing (EDIT) as Good. People just seem to stop buying after 5-6 years.
We get bored, I guess.