When playing pool, how does the cue ball always drop in the pocket and the others don't

When you make your shots, you have to think about where the cue ball will go, not just where the ball you are trying to hit will go.

l think you mean in the return pocket.

Look at them carefully - the cue ball is slightly smaller and it fits through while the others don't. Or, depending on the system, it can be larger, and not go through the drop that keeps the other balls. Either way, it is a different size and is filtered out.

for the same reason that your toast always falls butter side down

l believe what you mean is how does the cue ball go to the head of the table when you scratch, as opposed to dropping to where all the numbered balls go. If so, this happens because the cue ball is weighted differently and falls to a ramp where the other balls will just fall past due to their lighter weight.

Almost right the cue ball is larger
it does contain a metal core but its a magnet on the track that holds it
one or the other not both thats why a bar box has such lousey q balls in tourns we use blue dot s with open tables they dont return but you can play with them