o Addded 'why' to the site

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1422461 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/site/apt/index.apt b/src/site/apt/index.apt
index 000c1dc..13ff773 100644
--- a/src/site/apt/index.apt
+++ b/src/site/apt/index.apt
@@ -35,6 +35,16 @@
    It is not a 100% API compatible replacement though but a replacement <with improvements>:
    lots of methods got cleaned up, generics got added and we dropped a lot of unused code.
 
+Why ?
+
+   plexus-utils consisted mostly of code that was forked from various apache projects. From a licensing
+   perspective this code became "unclean" when it was forked to codehaus. maven-shared-utils is
+   based on the original from the apache sources.
+
+Why not commons ?
+    We would prefer code to use commons-* code where appropriate, but the plexus-utils became
+    slightly incompatible (different) from the commons over the years, so migrating is not
+    always a 1:1 operation. Migrating to maven-shared-utils is a 1:1 operation in most cases.
 
 Relation to Commons-*