I'm not advocating that any enterprise use this service. I run a WAN with 4 local sites (on a MetroE MPLS network) and a remote office via a VPN tunnel. So this is not my first rodeo.
I would never use a cloud-based WiFi controller for the very reasons you specify, and that means that if I need to remotely manage Wifi while I'm out of the office, I'm using a VPN.
A lot of companies don't have the same security concerns. That's all I'm saying. And some for those who, say, manage wifi access intended for the public at multiple sites, like a Hotel or coffeeshop chain for example, this might be just the ticket. They don't have to setup and maintain a bunch of individual controllers, and can centralize everything in one console, and let someone else maintain the server it runs on.