why sell cash flowing multi property

[Lenin Belangonda]

Hi, I am looking to buy small multi family.  Since this is my first venture i tried to gather as much information as possible before getting into it. From all i read, the financial ratios specifically cash on cash needs to be in 10-12% range.  This makes sense but finding such property seems to be very very hard ( im trying in phoenix and Las Vegas).  well this is not supposed to be easy, I understand that.  But if its so hard to find a good cash flowing property what would be the motivation of any one holding such property to get rid of it?    Whats making me more curious is many of the properties listed, when i check the price history is not selling for much more than what it was worth 10 yrs ago.  So why sell something thats producing income for less than what you bought?