Financial institutions will give you a mortgage for your real estate investment with relative ease.
Just imagine going to your bank and asking for a loan for your stock or bond investments, it just won't happen. Even getting loans for small businesses is difficult; you need a good idea, detailed business plans, and lots of luck.
On the other hand, banks actually advertise mortgages to get business. This is because banks know that real estate is a relatively safe investment. No other loan is as easy to get from the bank as a real estate loan.