Somebody like you or I might frequently max our our cellular connections, but I wager most users never do. And how would they? Streaming 4k YouTube videos onto a screen smaller than a postcard? It just won't make a difference for them.
This is the 640kb argument.
Being able to download a move at the gate? Potentially game changing. Being able to stream video from a drone or car on the road to centralised servers? Potentially game changing.
People with capital are willing to bet this technology has legs. Your not being able to figure out why is not a good reason to block the investment.
G5 will also reduce latency a lot, which is another vector that will open new possibilities.
Even as a techie, at some point I want to draw the line.