Yeah, LTE speed is very good, but it’s not easily expandable. To get very high speeds you have to connect to several towers or be very close to one with a high bandwidth. And, with increased bandwidth, higher resolution video, and more downloads and uploads will be supported. There are new applications that would saturate LTE infrastructure. Also, 5G is used for home internet service, which requires much more data volume than mobile devices do.

Edit: Additionally, 5G deployed in current LTE bands will only show a minor speed improvement, especially when only connected to one cell. It’s still confined to the limits of physics.