In short, because it´s relatively safe, and makes a good return on your investment.  One of the reasons that I decided to focus on investment properties, is because I believe that there is a great population of people who are working to secure a good retirement.  However, employer benefit packages are fading away and Social Security is still a big question mark.  Yes, there are IRA´s and 401k´s, but when you can get a 20% - 40% return the first year, there really is no reason to not invest in real estate.  Combine that with these facts:

1. Someone else is paying the mortgage on the property.

2. Rents increase over time as expenses tend to stay flat, so investment properties get better as time goes on.

3. Certain tax advantages are available to investors.

4. There is no more land being made.  While prices may fluctuate year to year, long term, based on supply and demand, value of real estate should go up.

Of course, there are some downsides to investing in real estate, like dealing with the maintenance of the property and finding good tenants.  But these downsides can be minimized by utilizing a good property manager.  For a low percentage of the income, a property manager can do that work for you.  You sit back, own the property and let someone else manage your investment.  Once you have a number of properties that have a positive cash flow, you have a good passive income for other things, or even more properties.  There is a reason people like Donald Trump are where they are3;real estate investing.