This the Ad Coelum Doctrine in legalese. I don't think it makes sense either.
Why wouldn't you?
You don't own the airspace over your house (over some minimum altitude), why would you own the land under your house (below some minimum depth). I would have absolutely no problem with a tunnel running 20m--or whatever the safe, silent amount is--underneath my house.
So you wouldn't have been okay with the Elontunnel, which runs closer than 20m below the surface--about 28 feet in the case of the Hawthorne tunnel. Though for point of comparison, some portions of the Metro system run at this depth or shallower.