Some things are torn down precisely so they will not be rebuilt, and to raise them again is to insist that the lesson which cost so much can be ignored. The curse binds the cost of rebuilding to a man's own children, which is exactly how it works in life. When we resurrect what was rightly destroyed, our sons and daughters pay for our refusal to learn.
The warning has nothing to do with mere stone and mortar. Jericho stands for a corruption that had to fall, and the man who reconstructs it is choosing the past that ruined him over the future that could redeem him. What you rebuild, you pass down. Refuse to let a defeated evil rise again, or your children will inherit the ruin you invited back.