Why is git so slow with large files?

I was trying to use git to manage my pictures (backup / take snapshots). The entire library is several GB. Most of the files are JPGs of 2-3M. When I was adding the files into repository, it seemed to be taking several days. CPU utilization was always near 100%.

Is there a reason why git should be slow on large files?

p.s. I know git was not designed for this.

Git by default compresses files. JPEGs by default are already compressed. It's not that it's large files, it's that it's compressed files.

You'll notice the same effect adding ZIP files to a git repository.

EDIT: There is an interesting thread on https://stackoverflow.com/questions/7102053/git-pull-without-remotely-compressing-objects about compression.