I really don't see any reason why a developer would want to work with Sony nowadays...
It's like a death sentence for your studio.
Unless you make good games. Most of Sony's first party studios were 2nd parties they partnered with during the PS1, PS2, and even the PS3 eras of their consoles.
This is Sony's first party process. They bring in a 2nd party studio, help them turn out a few games, if those games do well they offer to buy them and make them first party. If they don't they cut them loose.
Just so happens if you make a few mediocre games and Sony cuts you loose that the likelihood of finding another worthwhile publishing deal is pretty slim.
This also more underscores the inability of the management within these studios to conduct long term planning and budgeting. Sanzaru released the best game of the now endangered/dead studios and they had to cut payroll before the game even had a chance to do anything at retail. Superbot is talking about similar issues pretty shortly after their game came out too. This is a problem with management not securing a next step after the current project, either through poor planning or lack of ability to close a deal. You can't go looking for your next meal when you're hungry in any competitive industry.
As for the first party closures, I'd say most of them make sense.
Zipper wanted to move away from the SOCOM IP and were given their big budget shot with MAG. It failed. They then were given the chance to return to their base and bring SOCOM back, failed again. The writing was on the wall when they made Unit 13 because they had shown an inability to deliver a contemporary shooter that appealed to consumers in the same way as Battlefield and CoD. If they'd stuck with what they were good at and made the needed evolutionary steps to the SOCOM IP they might have established themselves as a major first party studio. It's a lesson to every developer who wants to try a new IP when the current IP is still going strong and not suffering from brain drain.
Liverpool closing upset me personally because I'm a big WipEout fan, but it's not like Liverpool was turning out a high volume of product relative to team size, they look to have had considerable staff turnover as it was (lead designer changes on all recent WipEout games is an example of this), and weren't a big retail power. So if you have Evolution located in Runcorn and they're bigger, where the group manager is located, and been more successful at retail why would you maintain a second studio all of 15 miles away? It's inefficient. Assuming the rumors that a bunch of Liverpool people moved over to Evolution that seems to only make economic sense. It doesn't mean WipEout is dead either, just that they were a part of the bloat you can trim down periodically.
BigBig just failed to deliver great games. Middling games with nice ideas, sure, but nothing that really impressed. Eventually you move on.
The standard for first party growth that I'd like to see from Sony is maturing their proven studios into larger, more productive, more bankable entities - which is already being done, and identifying their next wave of future first party studios.
Not having bought Insomniac is problematic, in my mind, though that is likely due to Insomniac's own choice. That situation might change after Fuse, we'll see.
Ready at Dawn not being purchased after their excellent work on the PSP is also questionable, though they do have "an exciting new IP for a Next-Generation home console" listed as their current project on the website. Note the singularity of that statement. Maybe MS swooped in and hired them up for a X720 game, but that seems highly unlikely. Sony giving them a full featured new IP early on with the PS4 to prove their metal seems like a realistic scenario here, and isn't too different from what they did with Sucker Punch.
Next they need to give The Workshop (Sorcery) and Tarsier (LBP Vita) another release or two to see what more they can do, both have promise.
Overall I'd say their first party studios are in the strongest position they've been in to date and if they identify some upcoming talented 2nd parties at the start of this generation they have the makings of a real break out.