Insider fact on why this makes sense. The intention here is not to make "physics based" because we are approximating a lot of things. The idea of having it named "physically based" is because it is as close it can get to reality but not the reality! So we will always be aware that we are just running a simulation not the real thing. The authors also make this claim in the introduction section. [0]

[0]: https://www.pbr-book.org/3ed-2018/Introduction