The enthusiast gamer need to except that we're in the middle of an industry shift right now. For decades the video game industry has been controlled by the publishers. Digital distribution and the popularity of smaller titles at lower pricing has built a pathway by which the key creative people in the industry can move out on their own and see greater rewards for the same risks that have always been there with going independent.
The power in this industry is swinging back to creative, and as a result talented people will not remain locked in with the major publishers (1st or 3rd party) if they aren't getting to do what they want.
I'd argue that of all the major publishers Sony has really been one of the first to recognize this. They aren't looking to lock someone in to their hardware, be that as a first party developer or as a contractually obligated exclusive. But the end result of that will be a lot of turnover.
Col Rodgers already explained why he left. It's unfortunate for him that he clearly still enjoyed the AAA genre and working for Sony, but for personal reasons couldn't make it work.
Amy Hennig and Justin Richmond left for what sound like creative differences with the direction Sony (and therefore the majority of Naughty Dog) have chosen to take the studio. This isn't a negative towards them or Sony, it's a positive attribute of the industry. The fact that highly talented people like them can actually opt to go do something they find more creatively appealing versus being stuck somewhere they aren't being stimulated is a positive.
Does anyone really want to see Amy Hennig spend the rest of her career writing Uncharted? The same woman who crafted Soul Reaver out of the original Legacy of Kain lore being tied to the popcorn flick equivalent of video games? Don't get me wrong, I'm not hating on Uncharted here, but it's just a waste of her talents. None of us would want to see Joss Whedon do nothing but Avengers sequels from here until eternity, or Chris Nolan only making Batman movies. Those are good films, but I'd rather roll the dice on getting another Firefly or Memento/The Prestige respectively.
The cornerstone of what has made Sony's first parties so good in the last several years hasn't changed, and that's a willingness to let the creative staff create. Sometimes that leads to projects going off the rails a la The Last Guardian and the cancelled Stig Asmussen project. Sometimes you can put them back on track (like SCEJA has been trying to do with The Last Guardian) and sometimes a few reboots still aren't enough and you've got to know when to fold 'em.
I would describe Sony's last several years as being a large number of solid games with a few gems sprinkled in. That isn't a sustainable ecosystem in today's AAA market, and that is why it's becoming clear that Sony is looking to consolidate their project roster around the talent who have produced their proven sellers.
For example, lets consider Sony Santa Monica's production over this last generation. They collaborated on about two dozen games over the life of the PS3 and only developed two internally. So now that Sony has a system that doesn't require nearly as much technical hand holding and are offering a far more open indie platform what sense does it make to maintain that same staff? SSM needs to be retooled. It was built for an era where Sony needed to go out of their way to seed all these smaller projects to compete with MS' Xbox Live Arcade offerings despite MS having the easier system to work on.
Now SSM needs to be a studio that can produce major AAA exclusives not named God of War. They've gone to that well one time too many already. They need to reshape their focus away from being the shepherds of other smaller studio projects and instead be a Naughty Dog/Sucker Punch type themselves.
Same with the recent layoffs at SCEE. There has been real need to scale back there for a while now. Cambridge is being fully integrated into Guerrilla Games. Of course there will be redundancy there. SCEE London doesn't need to spend nearly as much work showing people how to make the PS4 even work as they did the PS3, so of course there is excesses there that can be culled. Evolution added a lot of staff from the closure of Liverpool and the like a few years ago, obviously there was going to be some shake out from that unless Evolution grew into a two team studio, which Sony is clearly unwilling to fund until they have a more proven track record of success.
The studios that are growing are the ones who have consistently delivered multi-million sellers. Naughty Dog put out four of the best selling games of the last generation. What other studio has that prolific? People hate on Guerrilla Games but they delivered three multi-million selling titles on the PS3 and a PS4 launch title that has also sold quite well. That is what Sony is paying attention to here. Meeting deadlines matters.