If that's the case they would still get the software sales. The only issue with putting there games on PC is there more open to piracy.
The issue is that in that case they don't make licensing money from third parties anymore.
When you buy CoD, Assassin's Creed or whatever on PS4 / PS5, Sony takes around 15-20% of the money. So the way the system makes money is the more people buy a PS, the more likely they are to buy at least some third party games on PS, which makes Sony money "for free".
So even if a game like Days Gone doesn't break even on its own (I don't kniw if it did), if it pushed at least a few tens of thousands of people to buy a PS4/5 those people are likely to also buy a few third party games for PS or subscribe to Plus, which makes Sony additional money.
Moving IPs to multiplatform means making more money on the first party games themselves, but pushing less people to buy your console and make you money there through additional purchases.
As long as only old-ish games are being ported, you can argue that by now all those who could have been convinced by them to buy a PS4 already did, so you are selling those games to people who would have never bought them or a PS otherwise.
But if Sony start to let go of new exclusives on their brand new console, it means they started to move away from a proprietary platform model and into a publisher/service provider one.