(note: I do fly out of Goulburn, using John's planes)
My understanding is that it's basically "enforced courtesy".
If you've just landed and you can either backtrack down the main runway (22/04 in YGLB) or down the grass runway (26/08), taking the grass strip means that the bigger planes (that need the main runway) can takeoff or land immediately. If you insist on backtracking down the main runway then they end up going around (possibly more than once) waiting for you to get out of the way. Same as if you meet a Rex flight at an uncontrolled airport; if it's not much trouble to help them stay on schedule then you might as well do that.
There are lots of little things like that in the sky, on the ground, and on the water. Not legal requirements, but actions that make everything flow a bit more smoothly. The NOTAM is essentially a response to people ignoring this.
Realistically, nobody cares where you land as long as you don't get in the way of the skydiving planes. Since they're only in the circuit area for a few minutes at a time, this is not really difficult.
roundsounds - I may be wrong, but I think that's the list of information that has to be included in a NOTAM, rather than the list of reasons that can cause a NOTAM to be published.