It is very annoying to try and follow through minified code. I've tried to view the source and see what some extensions are doing but it can be a bit of a painful process. You can at least sometimes figure out what kind of GET/POST requests the extension may be making, but it's much more time consuming to try and ensure everything is safe.
The other problem is that the extensions can update. You typically get zero notification an extension was updated. Most extensions start off safe, but later get sold and used to farm data.
Formatting isn't the issue. Just more time consuming to try and read the code when it's all got garbage variable and function names. Not that you can't do it, just slightly more effort. Also the bigger issue I mentioned in my comment relates to the problem of extensions updating without any notice.
The other problem is that the extensions can update. You typically get zero notification an extension was updated. Most extensions start off safe, but later get sold and used to farm data.