That can be solved with tax/other laws. Guess who will be most impacted by those laws? Not people with one or two apartments as much, but those who do in large scale - that is again politicians and their helpers who help launder illegal money this way. If there are loopholes in the law, people will abuse it but we have to realize the loopholes are not meant for the layperson but the powerful few who abuse it at much higher scale.