For several years now, you have heard general economy market experts saying that a correction or a crash is coming. If you go to MarketWatch homepage, you probably see such an article on their website at least once a week. Additionally, because this bull market has been going on for so long (if I can recall, longest bull market in history), that people are anticipating a market downturn soon. Lastly, because the last recession in 2008 was so bad (worst recession in history) that a lot of people think that the next recession is going to be just as bad, when in reality, 2008 was an anomaly from in how bad of a recession it actually was. Most recessions aren't going to be that bad.
With those three factors in peoples mind, many who are investing with their own money are are scared of what they could loose, and not what they could gain. As a result, people are sitting on the sidelines waiting for the market to correct itself so they can come in and buy something at basement bargain prices. I think these people will be disappointed though when home prices don't fall by 2008 levels.
Personally for me, I only have a single family rental unit and am in the process of actively looking and buying my second. So long the unit cashflows even at a discounted rate (if a recession does occur) I will be buying. I think it would also be important for individual investors to hold on to more cash in the event of a recession, but that doesn't mean to hoard it or stop investing altogether; just increase the reserve amount a little.