Except that the physical book isn't the way people lookup facts these days.

The open book test is purposes is to not have to know all facts (formulas) but proving how to find them and how to apply them. (Finding is part of it as the more you look, the less time you got to use it, thus there is an optimisation problem which things to remember and which to look up)

In modern times you wouldn't look those up in a book, thus other research techniques are required to deal with real life (which advanced certifications should prove)

Going to university isn't how people learn these days, so there is already a real-world disconnect, fundamentally. But that's okay as it isn't intended to be a reflection of the real world.