It's a very good business. In many developed countries, there are very strong incentives for owning several properties. Once you've reached a certain level of wealth, it's basically free for your - since you're buying it with a mortgage. And quite often you can deduce the interest paid, from your taxes. We are effectively subsidizing this behavior, instead of taxing it.

Simplifying a bit - you want to put 100k$ to work, and you are wealthy enough so that the bank will lend you whatever you want. A great business is to buy another home, for say 500k$ - the rent and tax deductions will cover your mortgage, so you effectively turn 100k$ to 500k$ over the span of the loan. It's basically using your leverage, which first time buyers simply cannot most of the time. It's an unfair game.

In short - the system should be set up in a way that owning a second home should not be a good financial decisions - it should be an expensive decision. If you're rich enough and want to own a second holiday home - no problem. But in the current state of affairs, it's not expensive - it's actually profitable to do that.