The builds are compiled to save the user time ending up confused about what one can use.
It is a one-click setup comprising of all the stuff you’ll be needing to run Kodi in a way described by that particular build. It would be like buying a customized Jeep where you know what exactly you want as a package. The build/package may contain customizations like skins, codecs, settings and so on. Kodi Builds is like a complete package of everything you’ll need to use Kodi in a certain way.