40. Why not just narrow the target to residential property call it a tax on imputed rent?

The reason is because a major objective of the closing of the loophole in our income tax regime is to target the way businesses deploy their capital, namely to increase productivity. If you have a business that year after year makes lacklustre returns on the capital it owns, then that capital needs to be put to work more productively - either by the existing owner utilising it better or by it being sold to someone who can. Productive capital is a scarce resource, this policy will raise the supply to those who can get a return on it.