This way of thinking only makes sense if you believe, as Yochanan did, that “soon the Temple will be rebuilt”—and not just soon, but suddenly, without preparation. In other words, the Third Temple is not going to be a massive, long-term construction project, like the First Temple that Solomon built, and the Second Temple that Ezra and Nehemiah built. It is going to spring up or descend from heaven all at once, intact—and in that moment, Jews will suddenly have to go back to obeying a whole host of laws that currently seem obsolete. For this reason, Jews have to remain in training, ready to resume Temple life when the need arises; and the Talmud, one might say, is their training manual.
Earlier Daf Yomi columns are noted here and links.