For some reason the fact that intranets can significantly outperform Internets and in particular THE Internet is a shocking concept. It shouldn't be.
An intranet is a contained network managed to optimize the performance to meet the needs of the participants on the network. Your corporate network in your local office is an intranet. You probably have IT people working hard to make sure its up and as fast as they can make it.
Your home network is an intranet. Wired or wireless, you are probably able to get throughput that far exceeds the speed you get from your Internet connection.
The INTERNET on the other hand is owned by no one, optimized for no one. Whoever you buy your Internet connectivity from, particularly if you are a broadband customer, has a network that is physically, locally accessible through a persistent connection (as opposed to dialing in to a remote network). They do everything they possibly can to make it as fast as possible. Your speed and throughput is dependent on a variety of variables, the most important of which is the type of wire/fiber that connects your house to the network.
Their ability to control the quality of service and throughput you receive to your home disappears the minute your traffic leaves their network and is passed of ff on to the route that will take or request your bits to or from their destination.
Think of it as crossing the border between the USA and Mexico in a car. . Neither side cares about how fast the traffic of the other side gets through. If its busy, its busy. If its slow, its slow. Its not their primary concern.
This is exactly why your video buffers , websites timeout and downloads take forever. No one is responsible for making sure its fast.