There is literally no publisher that is actually worth the money from Sony's point of view. Surely MS can gobble up Bethesda and ABK and really not feel a thing just to shift the power position on the market, but Sony works more strategically. When Sony or MS buys a publisher, they are buying a competitor and the "value" of the IP and the publishing infrastructure is basically dead weight on the price. Take a look of the industry and you can bet that the executives in Capcom, Square Enix and similar big publishers are losing sleep every night over the next commercial flop with a 120m budget. What's the point of spending billions for those issues?
Buying studios however, is only a smart move. Let's say Insomniac - 230 million dollars. What do you get for that money? A few teams of extremely talented people with a great track record, of course their technology. Sony owns the R&C IP already, and whatever project Insomniac would have worked on, they would have needed a publisher anyway - SIE, MS or EA for example. Staying independent must have it's benefits, but also risks. Sony has even acquired studios that have just been formed that have not put out a single game yet.
Are there still any "big" studios that are possibly available to buy? Remedy, Kojima Productions? Both of them probably want to stay independent. Sony should rather be buying licenses to Konami IP to bring back fan favorites, and create new IP.
Honestly, I could see that this chain of events might make other third-party publishers relationships with Sony even better. Microsoft already has Call Of Duty, Doom, Overwatch and Halo as first-party titles. Why exactly would EA fight hard over Xbox players' attention with the next Battlefield game, and why would Microsoft even care?
