outside of clip mask
if there is a artwork with many points in clipping mask, mouse still snaps to anchor points of that artwork outside of the clipping mask. If i don't see that artwork outside of clipping mask, why snaps...
It's because the objects are still being rendered. You can check this by viewing in outline mode (cmd/ctrl+y). What Illustrator does is use the top object as a sort of alpha mask to hide the areas visually, but they are still there. The objects would have to be deleted to not be rendered and that would defeat the purpose of a clipping mask. They could maybe code something that would hide vector objects outside of the clipping mask from smart filters/snaps but I am unsure of how that would be done.