This is why laws should have sunset clauses
That would be the extra lights that have to be turned on at night.
If they are needed they can be voted upon again by parliament, and will no doubt pass.
In fact I would say not only should all laws have built in expiration dates, such expiration dates should be shorter the lower the percentage of votes in parliament it too to pass them!
If you can only get a 51% majority in parliament to pass a law, that law should not exist beyond that election.
It could be, to the contrary, that the legislators have come up with "straw bale" as something that simply does not belong under the bridge, in order to raise the brows of the people navigating the river, and make them wonder what's going on, all that in order to draw their attention. If so, it serves its purpose even more as straw bales are getting less common.
A bit tongue in cheek, of course - but I can't image the amount of unnecessary work regular continuation of _every_ law would cause. Time limits on laws are already a thing, but it shouldn't be a default.
I suspect the reason it's not in this case is because it's kind of an endearing tradition that people like. I don't think you can say much about "the law" in general based on this case.