The reason is that the apartment industry, unlike other forms of commercial real estate (retail, office, industrial), is heavily laced with liability. Laws are written to protect tenants during every step of their experience at an apartment community; from when they walk in the door to begin looking at apartments to when they are moving out. You must sidestep landmines of liability every step of the way.
You also deal with employees working onsite, another group extremely protected by state and federal laws. By the time you finish the course it is almost terrifying to think about how much danger is involved in owning or managing a community.
This is a large part of the reason why the market at some point will require a larger spread between multifamily cap rates (currently back at mania levels), and the risk free rate received from government bonds (where you have no management responsibilities beyond collecting your monthly bond premium).
As I have discussed in the past, I focus on studying and working in the commercial real estate sector today to prepare for buying opportunities I see coming in the future. As an owner of properties you must be able to manage the onsite manager, and the CAM designation strengthens my ability to do that. I believe the next real estate downturn will be far more severe than what we experienced in 2008-2009 (especially for the apartment industry which walked away mostly unscathed), and will represent the greatest buying opportunity of our generation.