Look, MS bought Zenimax, okay. We all get that and their competition gets it. Companies arent blind to their competition, even Nintendo is constantly monitoring what is happening in the scenes where they have no involvement in. A lack of action yet doesnt indicate that Sony just "doesnt care", or that they believe there will be no impact on them. They have better data than any of you to determine the impacts of the moves of their competition, and they are not blind to the fact that MS owns 20+ studios while they own 14. Sony arent ones to respond to any competition move instantly, and generally it paid them off well to not go into panic mode over everything the competition does, look at early last year when MS "was controlling the conversation" regarding next gen, but at the end Sony dominated the year in terms of exciting and selling their console. I'd argue that they "oversucceeded" to the point that the stock to demand difference is far more extreme than many previous console releases despite having the largest stock for a console at launch ever.
My point is, Sony are aware of the competition, they constantly think what is the best move for them to maximize their own success metrics, this doesnt mean that they will suddenly buy a publisher mind you, but they will know what is the right move for them.
The bigger problem here is that MS has convinced everyone that competition = acquisitions and huge acquisitions at that. Its not and it better not be because industry consolidation is something everyone will regret at the end.