Extensions are so broken. They can update at any time without your knowledge or permission. There is a whole market of selling extensions to malware companies so they can put malicious code in an update.

But besides that, most the extensions I use have serious bugs. I'd be willing to fix them, but there is no ability to do that. Chrome makes it difficult to view the code and there is no ability to edit it or copy it. Let alone submit pull requests to the author, unless they happen to have put the code on github also.