If you were posting 'bump' on a thread every 30 seconds, you'd get yourself in trouble for spamming. It's just going to fill the thread with a load of spam, make it impossible to find any discussion, and it helps nothing since it's not actually bumping the thread anyway since it would still have been at the top of the forum without all of those posted bumps given activity trends.
I think it's more of a common sense thing - a thread doesn't need a bump, for a start, when it's on page 1.
If you're the author of a thread, there's the bump thread button - now that does have restrictions. I think it used to be every ten minutes, although that may have changed. Again, though, there's really no need to bumping threads every ten minutes these days - that number was from a time when there were hundreds of people on the forums at once.
So basically if people use common sense, they won't run into problems over bumping threads - but they might if they spam excessively over a very short period of time like your example.
People spam bump in their merchant threads all the time and mods basically don't moderate consistently on it. There's tons of threads with literally hundreds of posts to bump it when they could just press the bump linkbring back the lumbridge pig pit