It allows you to reuse that structured content in many ways, everywhere.
(Django CMS as demonstrated in the video is purely about building pages, which makes it — if I'm being a bit harsh — just a glorified MS FrontPage.)
Even the demo http://demo.django-cms.org (good luck getting in at the moment, though) shows how django CMS can reuse structured data from multiple applications that also integrate with its editing and publishing tools (in the demo, news, people, events, jobs, etc).
There are biomedical labs for example that use django CMS to publish information automatically. Obviously django CMS itself knows nothing about biomedical data, but it provides the tools that make it very easy to integrate those applications (which thanks to Django are themselves very quick and easy to build).
Another example: https://developer.ubuntu.com/api/scopes/cpp/current/ is part of a django CMS site - and I can assure you that that API documentation is not coming out of a FrontPage-like page builder!
Where the video says "The Django CMS interface", the interface is clearly page-centric, not structured content-centric. It has building blocks like "feature-visual", "bg-home.jpg", "feature-content", "container", "row", "column col-md-24" etc.
How is that structured content?
Perhaps it can do structured content, but then why doesn't the video put that front and center? Is this perhaps an "also" feature, for building landing pages? Then why does the marketing talk about "content editors"?
So perhaps it's just the marketing that oversimplifies things? :)
I've been one of the skeptics on how big a change this was going to be for years, but now having looked at the delivered product I'm really impressed and really excited to move some old projects into it.
If you want more of a page based CMS, check out wagtail. Also pretty awesome, although in very different ways.
To then downvote, that's just sad.