• Developers have already got over the HD hump. A huge reason why most games were delayed last gen was because of difficulty programming in HD. Nintendo has ran into this problem this gen (I am not lying, they did). However this shouldn't be a problem in 2013...
• The architecture. The Cell was hell to develop for and Sony's stubborness didn't help. The 360 was  easier to program for but PowerPC is still not that great for programming. The x86 was supposed to make it easier to program for due to familiarity with architecture and all that jazz. According to Sony: "Sony’s Mark Cerny recently sat down with Gamasutra to discuss this decision. In short, the company moved to x86 to make it easier for developers to code on the machine." The Xbox One of course uses similar architecture.

everything changed when holiday 2014 happened

I would assume it is because people are trying to make more open world/open games which = increased development time. Like I am guessing that if they made games like last gen that were a lot less open just with better graphics, the games would come out faster but since this gen's theme seems to be big open areas or open world, I would assume that is the reason!

Plus learning a new OS and stuff isn't exactly easy so maybe after this year, it will be faster

Regardless of why it's been happening a lot lately, It's not like the whole industry is doing it. I think some studios and publishers know how easily they can announce games with the internet, yet became slightly self aware of how archaic early announcements have become. Given by the fact that studios like Sony's first parties, Bethesda and many others are still maintaining radio silence.

what happend ?

Games released earlier than they should with known shippaples (a.k.a bugs).

this

and this

With higher expectations doesn't make it any easier for the developers..