Because your devices are all individually installed and configured for a specific SSID and Password which can be different for each device if you run devices on multiple networks.
If you change either of these, every device on the network that changed has to be reinstalled to match the new SSID and Password.
DO NOT DELETE THEM FROM THE APP. Just reinstall them. That way you don’t loose any data from the MAC identified device.
There is a wishlist request to change this to an app based setting that can be reconfigured by the user for each\all devices.