Could someone explain it to me? Pretend there's a six-paragraph prompt with supporting details, brainstorm cloud seeds etc. below. 
I think the simplest way to think about it is: increased capacity.
While the idea of ludicrous-speed transfers to a handset/smartphone make no real sense (you can already stream HD video content with 4G, and really, what are you going to do with any other data?), remember that there is a whole lot of devices out there that will use a cellular network to communicate. For instance: cars. We all know about how Teslas phone home, but within the next ten years all new cars sold will have some kind of cellular data connectivity. (And when the carriers sunset it like they're doing with 3G, well, hahaha, you're fukced).
Another idea is that 5G wireless provides an alternative to fiber or cable internet.
[I was going to say, "no need to get rights-of-way to run cable/fiber" but the cell providers here seem to be plunking down their poles with 5G antennas wherever the fuck they want, and it would not surprise me if many of those towers were repeatedly vandalized until the point is made. And it's not about stupid fears of 5G, it's about companies putting their poles on private property without permission. (Why they can't share existing electrical poles like the incumbent telco and the cable company and the power company already do is baffling.)]
Anyway, just getting a 5G hotspot that does a gigabit rate and attaching the usual firewall/router to it would seem to make customer installations very simple. Of course the connection would be metered and the customers will end up being fucked anyway.
So the true answer: money for the providers, with a secondary feature of money for every hardware manufacturer up and down the food chain, from the backhaul/towers down to the handsets.