It's so that we can make cable companies obsolete without running fiber everywhere. 4G networks just don't have the capacity to support use for TV streaming - the hope is that 5G will.
We will have to run fiber to all those 5G hotspots. 5G is very short range, it does not extend access to anywhere that doesn't already have good access, it just makes it possible to run devices at higher speeds without being tethered to a wall.
Yup! It means fiber to the neighborhood rather than fiber to the home. The proposal is that fiber to the neighborhood will be considerably cheaper than fiber to the home.
I don't believe cable companies will become obsolete anytime soon, lol. There's a tendency to rely on cloud-stuff more and more, we stream video instead of downloading, 4k, 8k, we store entire collections on google drive and stuff. And even if you think 5G will solve all problems with the bandwidth — well, I won't argue, but there are plenty applications (like gaming) that require low-latency, which 5G will solve not.
Note that I'm not necessarily arguing that this line of thinking (5g will obsolete cable companies) is correct, only that that's why mobile operators want it so badly - they want you to be able to drop Comcast and give them your money instead.
That being said there's absolutely no reason why 5G (or even 4G or low Earth orbit Sat) couldn't compete with cable companies on latency. In many places 4G is already lower latency than existing cable networks.
Edit to add: 4G also already offers fast enough connections for 4K and in many places 8K streaming. It's the total capacity that isn't there - they have to put data caps on so people don't do all their streaming on their mobile connection. 5G is more about removing data caps than providing faster speeds.