Consider this:
PC doesn't have to be a competing platform for Sony. It's an open platform where any developer can exist. Sony can make it their platform just as easily as anyone else has. It would actually be easier as they already have a fanbase.
For years people have been playing Sony's games on PC for free through emulators and Sony has been left holding their dick in their hand with no real way to prevent it. If Sony opened up a Playstation front end similar to Steam, GOG, Microsoft, Origin, Uplay, etc, they could put those exact same games up officially and make money off them hand over fist. Just like the others you would require a PSN account and just like the others you'd always see games on the store ready to purchase. They would rake in a ton of money. As it is they're just leaving money on the table completely missing out on people that aren't interested in the PS5. For many the PC itself is enough, others have a Switch to complement it, etc. So if they aren't going to sell those people a PS5 shouldn't they at least try to sell them some of the software they make the most money on?
Sure I can get the game files off sketchy emulator rom sites (until they get shut down) for free and find ways to get them working, but a lot of people would be happy to pay money to not have to do the work and have the company that made them in the first place offer them working perfectly out of the gate.