Subversion is much simpler than Git (centralized is always simpler than decentralized). Being simple is not what made Git popular.

Git is popular because it is free, fast, works well enough, and was popular in some major projects.

Its major advantage for most orgs (those who actually use it in a centralized manner, with a corporate repo that everyone syncs with every day, unlike the Linux kernel team) as compared to Subversion is that it makes branches cheap and easy. The ability to work with history offline is also nice in niche situations, but definitely not the major selling point.

Its major advantage compared to Hg is that it is more popular.