I think it's about projected sales on PC vs lost sales of PS4 hardware and software. I bought a PS4 for Bloodborne, and have ended up buying a few other games here and there (God of War, Spider-Man) which aren't system sellers like Bloodborne, but I'll buy since I already have the console. Release games on PC and that revenue stream slips away, and it becomes about fighting for space against other games on the already congested PC platform.
Now, what makes no sense at all is just sitting on IP for consoles that are no longer in production or being sold on the high-street. What is the value of the PS1 and PS2 Gran Turismo games being stuck on the PS1 and PS2? Maybe they'll remaster them, but if they don't they're literally just sitting on games that could earn them cash by just porting them to PC. Demon's Souls is the same... And then there's the smaller PSN games that are first party but limited to PS3 or Vita. I'd pay money for Cuboid on PC, but, nope, it's stuck on PS3. And my PS3 is stuck literally on the other side of the world, and I can't play it. In this sense, Sony are losing money to people who'll just emulate the games on PCSX or RPCS3.