Their consoles sell and they get a ton of money from third party content on their system. MS going third party is giving Sony a ton of cash, as per the quarterly report 64% of software revenue for Xbox games was on PlayStation last quarter, and Sony get a cut of that. Sony make bank on having a closed system generating revenue from third parties, so they have a vested interest in maintaining this and as it stands are looking to become the only real player in the high-performance console market by the time the PS6 roles round. They will use multiplatform releases selectively to generate additional software revenue but in a calculated way that won't destroy their hardware sales, unlike MS.