Sony's first goal every generation since the PSOne has been winning game developers to their side. Game devs like large user bases, but that's only one aspect of why a developer picks a console. Sony's primary focus every generation is to get everything else right: development tools, hardware storage and performance, consistent controller design, software medium, and so on. They've had some misfires here and there (the Cell processor comes to mind), but they typically outperform their competition in all of these categories.
I think it's because Sony knows their customer isn't the gamer, it's the game developer. The game developer's customer is the gamer. Again, user base numbers attract developers, but Sony recognizes that user bases are driven by developer support. It's definitely reciprocal, but Sony's dominance comes from understanding that catering to the developer is paramount. That's why they've consistently created an environment that breeds killer apps. I can't think of another platform maker in the last 20+ years who's been better.
So after 20 years of building up that kind of leverage with developers, it doesn't make much sense to just give part of it away until game developers make it clear they need it.