To Rabbi Michael Abraham.

“The rule that when the reason is nullified, the enactment is not nullified”—I know this claim, but there is no logic in holding onto a rule whose reason has lapsed just because of the enactment itself. After all, that reason has no meaning without the rule. In this way, we are left with all the excess baggage in Jewish law with no benefit at all. There is also something insulting to the intelligence in this approach. The Author [Rabbi Yosef Karo] did not for nothing omit from the Shulchan Arukh the laws of the Temple and sacrifices, and laws that were irrelevant in his time. Would it not be proper in our generation as well to do a similar house-cleaning?

With respect, and sorry for the bother.

This is not a claim but Jewish law. Beyond the fact that this is the law, there is logic to it as a way of preserving stability, especially when there is no defined Torah hierarchy. Without it, anyone could decide to cancel whatever he wants. No legal system allows a citizen to violate a law even if, in his view, its rationale has lapsed.
Rabbeinu Nissim, in his homilies, raises a similar question about the obligation of a rebellious elder to obey the instructions of the Sanhedrin even when they seem mistaken to him. He explains that there is value in obedience itself—namely, stability. You are right that once there is too high a dosage of enactments and decrees whose reasons have lapsed, the system loses meaning. Therefore the Sages found ways to circumvent this rule. See my article “Changing Enactments in Our Time” and the third book in the trilogy.
The Author’s omission of the laws of sacred offerings has nothing whatsoever to do with our discussion. He did not change those laws; he simply did not include them because they were not applicable, and therefore we do not need a practical summary of them. A completely different matter.

And in a place where there is a rabbi or halakhic decisor,
was there also, in the time of the Sages when they instituted Rabbah’s decree,
the above concern that he might go to an expert and carry it in the public domain?

I didn’t understand the question. When they enacted it, there was apparently such a concern.

In my humble opinion, he simply meant to ask:
What is Rabbah’s concern in a place where there is a halakhic decisor?
Surely one would not come to carry the shofar.

A decree is made in general terms, and we do not distinguish between cases. Beyond that, even a halakhic decisor can make a mistake inadvertently. Incidentally, specifically here they did distinguish between Jerusalem and the place of the assembly/religious court, and other places.