Neverclick dev here. It's not random, a lot of thought went into how the key combinations are generated and assigned.

When Neverclick generates the key combinations, it prioritizes keys in the center of the keyboard. It then sorts the key combinations from most to least convenient (so for example JJ and FF would be at the top of the list). It then assigns the most convenient key combinations to UI elements closest to the center of the screen because that's where people are most likely to want to perform a mouse action.

As the other commenter already said, with dynamic data, you can't really make things repeatable. However, it's still really cozy to use and way better than if it were randomly generated and assigned (which is how it used to work before it was updated to the new system).