I don't think you're looking at this from the context of a business model. Sony is basically asking itself: Do we want to run a software development arm or do we simply want more games for Playstation. If they simply want more games for Playstation then it makes sense to nurture certain talent, fund development/publish, but keep them independent.
Why? Because you don't have to actually run the studio. You don't have to worry about Recruiting, HR function, real estate, etc...you bring the check book, set the terms, and the independent developer gets it done.
Now can they just run off after a successful project? Yes. It's a huge risk but what's also a risk is putting all your capital up to run a studio because those costs don't just disappear if a game is a dud.
What if I get a 10 year lease on a building for a smoking hot studio but they have severe attrition and the next couple releases suck balls and I'm in the negative financially...now I gotta disbanded the studio and figure out the lease, office furniture, utilities, etc.
If I simply publish the game which means I own the IP, I don't have any of those worries. I just set the expectation, cut the check, and have my goons do progress checks or maybe even have my own staff embedded in the project.
In the end, both models can work but both can fail as we saw Microsoft flounder with "owning the goose" aka Bungie, Rare, FASA, Lionhead,etc and we seen them flounder with owning the IP "PGR".
