Gradle allprojects in React-native

I know a thing or two about JS and react-native. I was trying to comprehend the JAVA config of RN (by going through the Android docs in google developer training)

In this Section, The author have written following line

If a dependency is something other than a local library or file tree, Gradle looks for the files in whichever online repositories are specified in the repositories block of this file

I am Unable to comprhend the above line.

Also, In my current react-native project, it looks something like this (build.gradle)

allprojects {    repositories {        mavenLocal()        maven {            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm            url("$rootDir/../node_modules/react-native/android")        }        maven {            // Android JSC is installed from npm            url("$rootDir/../node_modules/jsc-android/dist")        }        google()        jcenter()        maven { url 'https://maven.google.com' }        maven { url 'https://jitpack.io' }    }}

Where as in project created by android it looks like this

allprojects {    repositories {        google()        jcenter()    }}

Can someone explain the difference? what is

        maven { url 'https://maven.google.com' }        maven { url 'https://jitpack.io' }

And

        mavenLocal()        maven {            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm            url("$rootDir/../node_modules/react-native/android")        }        maven {            // Android JSC is installed from npm            url("$rootDir/../node_modules/jsc-android/dist")        }

Why does RN people have them like this when compared to Android project created by android studio