Why was no hammer or iron tool heard in the house?

The chapter doesn't give a reason, and this answer doesn't supply one. It says where the work was done: "The house, when it was under construction, was built of stone prepared at the quarry; and no hammer or ax or any tool of iron was heard in the house while it was under construction" (6:7). The stones were cut. The chapter before says "they cut out large stones, costly stones, to lay the foundation of the house with worked stone" (5:17), and the builders "cut them, and prepared the timber and the stones" (5:18). What 6:7 says was missing is the sound of iron in the house. In Hebrew, 6:7 shares three words with the law for the altar on Mount Ebal: even, "stone"; shalem, 6:7's "prepared" and Deuteronomy's "uncut"; and barzel, "iron". "You shall not use any iron tool on them" (Deuteronomy 27:5); "You shall build the LORD your God’s altar of uncut stones" (Deuteronomy 27:6). Joshua 8:31 has all three words too. But those verses are about an altar and about iron on its stones, and 6:7 is about the house and what was heard in it. 1 Kings doesn't mention them. Exodus 20:25, also about an altar of stone, has neither shalem nor barzel: its words are gazit, "cut stones", and cherev, "tool" (tap prepared).