Not exactly decentralization but distribution was the main selling point.
In comparison to SVN and other non-DVCs git did not need to continuously talk to the central server for history, "branch" creations, unlocking/locking files before changes, etc.
Linus wanted a DVCS, but they wanted centralization and licenses were expensive, so he decided to launch the git initiative where he provided scaffolding and the rest came from contributions.
It was a selling point. Maybe even intended selling point. But it absolutely isn't the main selling point. Never was, never will. The big thing, the reason people ever started talking about Git outside Linux dev team, has always been branches. It's branches, not distribution, that made every SVN user in the world abandon it in exchange for Git. Saying distribution has been more important than branching is like saying automobiles replaced horses because of smell. Which, admittedly, was a big problem with horses, but come on.
Back then, when working with SVN, we had sites in various countries, with under provisioned VPNs between them. Loading up a single file history could take 15 minutes. I am not joking. Every single operation took ages, so really, any DVCS would have won in that situation, regardless of its approach to branches.
If the SVN server would sit in the same building then I guess the branching would have been the main selling point, but it was not the main selling point for us in that situation.
In comparison to SVN and other non-DVCs git did not need to continuously talk to the central server for history, "branch" creations, unlocking/locking files before changes, etc.
Linus wanted a DVCS, but they wanted centralization and licenses were expensive, so he decided to launch the git initiative where he provided scaffolding and the rest came from contributions.