Renaming an ESPHome device without immediately installing new firmware could leave every later upload looking for a network name the device did not yet use. Device Builder remembers the old name so an installation can still reach it, instead of requiring the maker to rename the configuration back.
J. Nick Koston covers rename commands and direct edits to the device name. The remembered name is a fallback when the new one cannot be found and is cleared after a successful installation. Devices using only the web server still need to be discovered under their new name before an offline status can recover.