git doesn't necessarily handle large binaries well (less true in recent versions). Also, when using Maven (etc) you can upgrade libraries just by bumping up the version # rather than hunting down the new jar manually. You can also use the same cached jar in multiple apps/modules rather that committing it in all of them - good if you've got a modularised application.

There are also other benefits like automatically downloading and linking sources and documentation (more relevant if using an IDE).