The could buy companies if they want. They bought Bungie for $3 billion. And all they do is basically Destiny. Someone posted a market valuation list earlier this year and UBI was $8 billion at the time and all the Japanese companies were less than that. The big ones like EA and T2 were around $20 billion I think so those are out of reach, but the Japanese ones arent. They could had tossed in an extra billion and gun for owning Sega, Namco or which ever other Japanese companies were close to Bungie. But they chose the one with the smallest game library, least amount of control (Bungie supposedly keeps their leadership team and choice of multiplatform development), and it's the studio with an all or nothing focus on MP GAAS. So with that, you can see Sony is aiming for GAAS model games vs. breadth of game franchises.
In 2018, Sony spent $2 billion to buy up the rest of EMI (music) so I think they now own all of EMI. And that's when they werent even making around $10 billion profit/year (was $12 billion a year ago). So they got the money to buy any game company they want except EA and T2 which are way higher in price and out of scope.