5G can handle more clients. WiFi (vaguely) slows down if a slow client connects to the same network as you, rather than a fast client using all the bandwidth.
Cellular ISPs also don't do routing the way wifi/wired ISPs do, so your IP address isn't tied to your physical location anymore. That wouldn't apply to private 5G so much though.
Still, I'm confused. The article says that both WiFi 6 and 5G have similar theoretical max speeds. The main difference in the article seems to be that 5G operates on licensed spectrum. But if I understand correctly, this AWS service uses an unlicensed spectrum, so I'm still not sure why would I choose this over WiFi.