https://artsandculture.google.com/asset/self-portrait-with-g...
But exhibitions change all the time; it would be hard to keep a virtual walkable museum up-to-date with the real-world one. Plus it'd require more headcount, and more powerful gpus on the viewer side, and more edge cases wrt operating systems and browser combos to test.
I saw videos of a penguin walking around an aquarium in Chicago going around, and I found that gave me more of the feeling I was looking for.
Some museums have amazing architecture and feel (The Foundation of Joan Miro in Barcelona is a great example) and having that feel represented by a proper walkable 3D environment would greatly enhance the experience.
I'm a bit concerned though that simulated museum visitors may break the immersion -- we haven't crossed the Uncanny Valley yet.