Because that person no longer has any personal stake. Suppose the tenant was good. In the worst case, the landlord won't remember them. But if the tenant was bad, the landlord is no longer renting to them, and therefore doesn't need to see them gone.
Think about it: If you were a landlord with a problem tenant, would you give them a good reference? If you do, they'll move out and you're free of them. If you don't they'll probably figure it out and their resentment will make them an even worse tenant.
Employment Background Checks work in a similar way, except most people don't bother taking that extra step. They ask for references. References that are probably biased or have a stake in getting rid of the person.
So suppose you have a position of trust, responsibility, or sensitivity. What can you do to get a fuller and probably more accurate picture of the potential new employee? You can use the property manager's trick of asking someone who is no longer a stakeholder.
Two possibilities are:
- When you are provided a reference for a current employer, you can try asking who has directly worked with the person and who else you can speak with off the record.
- After the person has been hired to a new position and has cut their ties with their previous employer (but before they have completed their probationary period), you can call up that employer again and ask if they would like to revise their testimony, now that they can speak more freely with no fear of on-the-job reprisal from an employee.