It's a tragedy of the commons situation. You can share yours and nobody shares theirs, so you lose a bit. You need a large number to make it work effectively.

It's a tragedy of the commons situation. You can share yours and nobody shares theirs, so you lose a bit. You need a large number to make it work effectively. I personally never feared sharing my salary, but even after that not a single person ever in multiple jobs shared their salary with me.