Why are extensions project based and not global?

[Jordan Zimmerman]

What is the reason that .mvn/extensions.xml has to be added to every project? 
It would be much more useful to add it globally in the .m2 directory. If I want 
to standardize, say, on Groovy polyglot I don’t want to have to have every 
developer in our org remember to add the extension to every project. That would 
be a big pain.