Why is Google Analytics tracking minified to:
// instead of: which saves one byte
// or even: which saves 3 bytes
No, no reason at all. In fact, Google Analytics recommends version #3 in their alternative async tracking snippet.
The most likely answer to your question is that a human being was responsible for writing the original snippet, and a human being didn't quite get the 100% most optimal minified version of it. In fact, you can also leave out the
a.async=1 part too because all dynamically injected script are async by default.
If you want to change it to save 3 bytes, go ahead. No browsers in use today will fail on your #3 syntax.