You're oversimplifying with that statement. There are many reasons why housing is scarce, and that is only one of them. - Existing homeowners trying to prevent

You're oversimplifying with that statement. There are many reasons why housing is scarce, and that is only one of them. - Existing homeowners trying to prevent denser/more housing - Regulations and codes that make building much more expensive - (As you noted) existing housing being wasted as an investment and I'm sure there's much more.