Why is 4G not enough and what are the use cases of 5G?

Surprised no one has mentioned IoT yet.

The goal is to have everything connected to the grid. Your door opens: it pings a server, you walk in through your main entrance: A notification is sent.

Not just in home automation, but in industrial settings as well.

There's a lot of heavy machinery equipment and industries ripe for disruption as IoT devices scale into those industry verticals. For example: real-time access to information about machinery running the supply chain is invaluable. Whether it is ground, air, or ocean freight, being able to tell when a shipment is loaded, when the carrier has arrived, etc... helps optimize a supply chain and allows operators to react in real-time to address supply and demand. Everything will be tracked whether it's an NFC or RFID sticker, and IoT devices will pick up these trackers as they flow through a system or supply chain.

In short 5G enables IoT devices at scale that can feed data into BI systems can let you find bottlenecks and react in real-time to issues that have a high impact from a deliverables perspective and might require intervention to correct an issue in real-time.

4G does not have the bandwidth capacity to enable IoT devices at scale.

The end goal is to finally kill local storage and have everything as a service, on the cloud. This way tech companies will finally take back the control on their users they have so foolishly relinquished in the 70s.

5G has extremely low latency, enabling anything that would benefit from that: gaming, telemedicine, low-latency video calls (could potentially allow live music collaboration over video chat, for example)

The use case is to allow telcos to put cable companies out of business with millimeter wave antennas to the home. Basically rebuild the bad old AT&T.

5G is critical infrastructure needed to beat the Chinese. Go America. So it gets to bypass pesky state utility regulation.

5G gets us to Gigabit speeds over the air, which 4G couldn't pull off even in ideal conditions. This introduces an incredible amount of opportunity that was not previously available (such as TV and internet for the home over cellular that's actually viable).

I’m invested now, I want to know how many Gs the marketing people are going to try and pack in there.

Let me answer by rewriting your question:

Why are stiffy drives not enough and what are the use cases of CD-Roms?