Like I said if these measure are so very good for our country, why deny that goodness after three years?

Mostly for the same reason that sunset provisions are usually included in bills - to create a mechanism to force the parties to come to a deal if it turns out that those measures end up not being "so very good." As we've discussed, international law prohibits countries from returning refugees facing persecution back to the countries they're fleeing. It also requires that countries give refugees basic due process - a right to have their claims heard. Denying refugees even the opportunity to make a claim is probably a violation of international human rights. It's one that we can plausibly try to get away with and hope that it doesn't have too much of an impact on our own foreign policy interests, but it's one that you don't necessarily want to make a permanent and binding decision without trying it out first.

Plus, those provisions are intended to address a new situation - the unusually high numbers of asylees that have been hitting the borders lately, within the last five years. No one knows whether that's a short-term phenomenon that might be ameliorated or eliminated once the "layover" of a few years gets taken out of the asylum system, or a longer-term phenomenon. Again, in those contexts, its very common to have a sunset provision.

Even so, I found a way to be OK with that figuring the debate and amendment process will improve the bill to be passable. But even short of passing, the debate would help voters better decide who best represents their interests in this issue.

That's not how reality works in the Congress, though. Senators will come together and negotiated and trade and debate on a bill that has a chance of passing - they'll take a hard vote, or be willing to make trades of positions, in exchange for the change to get an adopted bill that has provisions they want. They're not going to do that on a doomed bill. Once Johnson made it clear that he wasn't going to put the Senate bill on the floor, no matter what it said, then that killed the process. No one's going to engage in actual negotiations if it can't even get started in the House, because none of the Republican Senators who might be willing to take some political heat for a less-than-perfect border bill (in the base's eyes) if it got passed will be willing to take that heat for a bill that won't go forward.

Johnson's statement killed the bill. We can argue about whether he was wrong or right to do that, but once the Speaker says the bill isn't going to get put on the floor, you're not going to have anyone in either party being willing to swallow something for the sake of a compromise. Which means they're not genuinely going to spend any time or effort in debating or amending, either. Which is why McConnell stopped the process - he wasn't going to leave Lankford out there to twist in the wind.