Why does Joint & Several Liability exist?

This legal loophole acts as a safety net for landlords if one tenant decides to move out or default on their rent; however, it leaves the tenants and their parents in a very vulnerable position.
   
Most of the time tenants barely know each other well enough to be confident no one will be unreliable at paying their rent, it is largely blind faith.
   
In the situation when one housemate decides to leave or stop paying their rent, the landlord can legally look to the rest of the tenants and their guarantors to cover the shortfall. It’s important to know who you’re living with and if there is trust there in case of an unfortunate situation like that.