It might appear so but it is not. The game evolves and the building are also assets and part of the investment. Selling them should ensure you a pretty good ROI. But as I see it you need to get to a certain amount and you can let your city product for 2-3 months and I think you get all your investment back. From that point on you can either continue and get real ROI or develop the cit more and more. But I think it is addictive and is hard not to want to grow...