@dafish 

The change password you see under Me and View Accounts is just the Kasa Account password.  This does not change the link to the network the smart home devices are connected to.  For that, you have to do a factory reset on each device.  This will allow you to link the smart home devices to a new account and a new network.  Kasa does not have a way to transfer devices to a new Kasa account or a new network without a reset.    

  @dafish 

To be completely honest this is how our products have always been.  TP-Link doesn't manufacture products with transfer in ownership in mind, especially since warranties don't transfer.   Additionally, using credentials from a previous owner is a huge security risk.  While most people are honest and genuine there are others that aren't and using a previous owner's credentials could lead to a comprised network and is not recommended.  Kasa products can be very easily transferred it requires the original owner to remove the devices from their Kasa app and then reset them to the factory.  This will allow the new owner to create a Kasa account and set the devices up using said account and their network.  It might be inconvenient if you have a lot of Kasa products and you don't want to take the devices with you, but its all that can be done.