Because the devs might say, "we can't be arsed with this," and then everyone buying a PS4K on the promise of better software gets none. Sony can't make third parties provide a decent experience on their consoles (other than paying for it)! A purchase of a new console is always on faith and could go awry. One of the reasons people bought into PS3 was because Sony had earned a reputation with PS1 and PS2, instilling confidence that the platforms would receive lots of content.