There is a lot of reasons because it set precedents to for new Sony first-party games:
- Decreasing quality due being focused in multiplatform development.
- Less specific use of platform features (I don't know what features PS5 will have but the changes to use it going multiplatform is near 0).
- Less PS5 sales and so less user pool for multiplayer games.
- PC games mess up the consoles multiplayer.
- Less focus in PlayStation ecosystem.
I can go on.
It will just become like the bland and boring platform that everybody hates.
Maybe the way now is go Nintendo.
It is a huge mistake too... exclusives take Sony to the top and now they will just open again to failures.
I believe they will lose sales and userbase.
You can forget Sony games selling over 10 million being released on the small PS5 userbase and PC.