This video doesn't consider the physical layer that makes up the internet. Miles of copper wires and undersea cables are responsible for making this physical connection. If you were to cut major undersea cables that connect the U.S. with Europe, for example, the capacity of the North American network to Europe (and vice versa) gets cut by a large amount, enough to overflow remaining network pathways. Eventually if you cut enough cables you can pretty much shutdown internet access for entire regions.
Also, inland ISPs depend on a series of backbone networks that serve as large hubs/conduits to other connected networks. Cut those out and you also begin disturbing traffic for entire regions.
The internet is anything but decentralized.