It doesn't, the Adguard developers just chose to write their app in such a way that their main app (which is an Electron app) needs to be in the loop for everything.
Actually it's true - Adguard needs to run as a standalone process that lives in the menu bar in order to work properly with Safari. This permanent process does appear to be Electron based.
My guess is that it's engineered like this to simplify their code base(s) between their various free plugins and their paid "Adguard for Mac" and "Adguard for Windows" apps.
