Why doesn't git commit -a add new files?

Question

I\'m a bit new to git, and I fail to understand why git commit -a only stages changed and deleted files but not new files.

Can anyone explain why is it

Answer 1

Kelly is correct but I think another factor is that so many people expect that behavior because CVS, Subversion, and most other tools do it that way.

If Git committed new files, you might notice that you had committed .o files long ago and even worse they might harm the build.