They only have to target a single hardware configuration, the os has much less overhead than a typical desktop os, a graphics api that runs closer to the metal (also why the ps5 outperforms the more powerful series x) and some good development tools all go a long way to boosting the performance of the hardware.
I have an r5 3600 with an rtx 2070 and would not be surprised if the ps5 performs better with multiplatform titles.