Why aren't the Android SDK Jars in any Maven Repository?

Google blocked it. From this link:

The Android artifacts have been built and published to the Maven repository through the efforts of the Android for Maven project. Google prevented the official Android jars from being uploaded to Maven, so the, third party, Android for Maven project was started to provide an API compatible Android artifact that could be uploaded to the Maven repository. There are now artifacts for each major Android version available in the Maven repository. These are not functional, however, and only provide stubbed implementations of the API. All methods in all classes throw a runtime exception. Because an Android app runs on a device, it will never use these libraries for execution, but the API compatibility allows an app to be compiled as if it were the real library.

Google now has an official maven repository announced at Google IO 2017.

buildscript {    repositories {        maven {          // Google Maven Repository          url 'https://maven.google.com'        }    }    ...}

What's New in Android Support Library (Google I/O '17)
https://youtu.be/V6-roIeNUY0?t=3m34s

What's New in Android Development Tools (Google I/O '17)
https://youtu.be/Hx_rwS1NTiI?t=20m05s

Google's Maven repository
https://developer.android.com/studio/build/dependencies.html#google-maven

Migrate to the New Plugin
https://developer.android.com/studio/preview/features/new-android-plugin-migration.html

I found a better solution, using the common libraries delivered by SDK, I just used Android Home as repository in the pom.xml.

 <repositories>    <repository>        <id>com.android.support</id>        <url>file://${env.ANDROID_HOME}/extras/android/m2repository</url>    </repository></repositories>

does work for me now.