You are using

other people's money (in this case the Bank's), to do the things you otherwise would not be able to do (or enjoy the house you are living in). The bank, of course wants to earn some money too. Everyone got what he wants.

In this case, you are still MAKING 1W, right? Thanks to the bank that help you do that. So if you have 10 this kind of houses, then you make 10W, correct?

Of course, there are many other factors to consider, such as you don't pay too much to the house, and you may have better ways to make a return on your money, etc etc.