I know those are the most common reasons I hear, but they're just not believable to me.

. $200/month/unit seems to be a common example).

The common theory is people “wait” for a crash but when it comes, they are unable to act because of fear or lack of liquidity or often both.

Also some Multifamily Properties the  landlord pays the electric and gas for the common areas like stairwells.  

(Like common steps it took to acquire)

What's more common if the condition of the place is terrible is to get a $100K-assessed place down to maybe $70K if you paid $50K of so for it.

It appears to be common for many of the buildings to be divided into many rooms boarding house style and you pay for a room w shared common area.

This is very common in Southern California, and developers have been pumping out new construction left & right to replace the current market that's filled with old, deteriorating buildings from the 1960s. 

HOA's usually only have control of the outside and the common grounds of the property. 

If you find someone that will "do it all for you" - turnkey - they're making significant money off the deal one way or another, commonly on the spread of the purchase and sale of the property.