If REITs are giving such high returns, why should we even look at other assets like SSBs or fixed deposits? These give lower returns than REITs dividends.?

There is a higher level of risk with REITs. If the property market crashes or even slows down then your fixed deposit is not likely changing till interest rates change while your REITs are going to move. It's all risk management. As long as you are comfortable with the risk, understand it and can stomach it then REITs will give you better yields. Fixed deposits are very low risk, hence why the payout is low.

Simply put, they are less risky investments which ensure its value even in a downturn :)