I was maybe a bit sloppy when I said it "quickly drops to 0" instead of it "quickly tends to 0". It'll of course always be positive - in fact if N is the sum of the absolute value of the three coordinates of its current position, the probability of returning to the origin is strictly greater than 1/6ᴺ.

But it does tend to 0 in such a way that the probability of its random walk ever returning to the starting position is not 100%. It has a 34% chance of ever getting back at the very start of its journey - but if it gets too far off track that probability is going to tend to 0 fast enough that it's not likely to ever make it back, even with infinitely many steps. Here's a youtube video (that I did not watch myself) that seems to go over the topic.